e20 Lite 0.5 Vehicle Combat

[lucasjung]

I've finished reviewing the portions of e20 Lite v 0.5 relevant to vehicle combat (mostly from the perspective of aircraft, but also more general). Here is my feedback:

I really like the way the vehicle rules turned out. I especially like the mechanic for changing altitude—it really captures the feel of trading airspeed for altitude. But, I still have some comments:

Vehicles Table:
On the vehicles table, we need a note for minimum flying speed (i.e. stall speed) for fixed-wing aircraft.

External Stores on Aircraft:
I like the way that the increased drag from external stores is represented by a weight multiplier for calculating encumbrance. However, 5x is probably a little steep. These weapons are designed to be very aerodynamic, especially missiles. In fact, wingtip-mounted missiles actually decrease induced drag by mitigating vortex production at the wingtips. I would change the modifier to x1 for missiles and x2 for all other external stores.

Missiles in the Weapons Table:
These need some serious work. The missiles listed have pretty good ranges for, say, anti-tank missiles, but even the super-heavy missile has woefully short range for any kind of anti-aircraft missile, anti-ship missile, or many other types of missiles. The weights also seem kind of whack, but I’ll have to look up some numbers to be sure (I think the progression of weight increases from one size to the next is too flat). At each size category, there should be a number of different missiles available, each trading range and damage off against each other (if you take up more space for propellant, you have less space for explosives, and vice-versa). I’ll post a suggested table of missiles later.

Rockets vs. Missiles:
I would change the way missile guidance systems work. I would give every guided weapon an intelligence score, and any attack with a guided weapon uses the weapon’s intelligence instead of any of the operator’s abilities. The operator’s skill bonus would still apply, only the ability score would come from the weapon’s guidance system.

The major advantage of a guidance system would come into play when the missile will take more than one round to reach the target (i.e. when the range to the target is greater than the missile’s speed). For unguided missiles (aka rockets), the operator must target a particular square, and the attack roll is only made if the target is actually in that square when the rocket reaches it. If the rocket has a proximity fuse, it can make an area attack centered on the target square if the target is in an adjacent square. For guided missiles, some sort of skill check is made each round to see if the missile is able to continue tracking the target (this gives the target a chance to “break lock” by maneuvering and employing countermeasures), and the attack roll is made if and when the missile gets to the same square as the target. This same system could be used for guided vs. unguided torpedoes.

Determining Range in Three Dimensions:
I suggest the following modification to represent the effects of altitude and gravity on weapon range:
If the target is lower than you, the range is equal to the horizontal or vertical distance, whichever is greater.
If the target is higher than you, the range is equal to the horizontal distance plus the vertical distance.

Hard Turn Maneuver:
I think the DC should scale according to the number of squares you’ve moved relative to the number normally required to make a turn. Maybe DC = 10+[number of squares moved]-[number of squares required to be moved].

EDIT: I badly misread the rules for loss of control in regards to aircraft, and so my feedback was not good. I've modified it accordingly.
Out of Control Flight:
The rules for airplanes actually seem to model loss of control reasonably well, but an out of control helicopter needs a slightly different set of responses because of the complex relationship between yaw and collective (crudely speaking, collective controls the up and down motion of the helicopter; it is analogous to throttle). In reality, what happens can vary widely depending on the design of the helicopter, but here's a simple system which captures the spirit of what happens:

• On a d6 roll of 1 or 2: the helicopter turns left 45 degrees, reduces its declared speed by one category, and decreases altitude by a number of squares equal to half the minimum for its declared speed (if declared speed is zero, descends half its base speed).
• On a d6 roll of 3 or 4: the helicopter does not turn, maintains its current speed category, and decreases altitude by a number of squares equal to half the minimum for its declared speed (if declared speed is zero, descends half its base speed).
• On a d6 roll of 5 or 6: the helicopter turns right 45 degrees, maintains its current speed category, and maintains altitude.

On the topic of out of control flight, I would add two additional traits that some high performance jets could have:

1: “thrust in excess of weight.” It's kind of a mouthful, but that's the actual technical term that's used to describe it, and I've never heard any kind of nickname or shorter version. Basically, some jets have engines so powerful that they can point straight up and continue to accelerate because, as the name implies, the upward force produced by the engines exceeds the downward force produced by gravity. Such a plane is still subject to losing control due to stall: although airflow over the wings is not needed for lift in this situation, airflow over the control surfaces is still needed to keep the plane pointed in the desired direction.
Game rules: When an aircraft with this trait determines its current speed at the end of a turn, if, during that turn, it climbed, did not descend, moved less than its base speed in squares, and spent at least its base speed in movement, its current speed is considered equal to its base speed.
Basically, it can't stall as long as it stays pointed up with the throttle firewalled.

2: “vectored thrust.” An aircraft with vectored thrust is able to remain in control even after the wings and control surfaces have stalled.
Game rules: An aircraft with this trait is able to move at speeds as low as one-half its base speed without losing control. When doing so, it cannot climb, but instead descends one square in altitude for every square it moved less than its base speed. If the aircraft also has the thrust in excess of weight trait, it can climb when moving below its base speed and does not automatically lose altitude.

Scales:
I really like the set of scales, but I would change the names a little, to reflect terminology more commonly used in wargames (and war, for that matter):

• Character: 5 ft/square
• Tactical: 50 ft/square
• Operational: 500 ft/square
• Aerospace: Varies

This lines up well with the “What Fits on a Map?” sidebar: a platoon-level firefight would be considered a tactical action, while battalion-level combat would be at the small end of operational actions.

Sensors:
I like the idea of giving vehicle intelligence to represent computers and sensors, but I think this needs to be broken down a little bit more to represent different types of sensors. An attack jet might have an air-to-ground radar that is great for navigation and for targeting tanks, but which can’t process returns from other aircraft. A helicopter might have a dipping sonar that can find submarines, but which is absolutely useless for anything outside of the water.

EDIT: changed the names of most of the perception types.
I propose that we implement a list of perception types, similar to the list of damage types:

• Optical: Light in the visible spectrum, plus non-visible light which behaves similarly (i.e. Ultra Violet).
• Acoustic: Vibrations propagating through a physical medium (e.g. hearing)
• Chemical: Trace amounts of characteristic chemicals suspended in a fluid medium or on the surface of a solid (e.g. smell and taste).
• Thermal: Infrared Radiation
• Radio Frequency (RF): Electrons propagating as waves (e.g. radar)
• Electromagnetic: Fluctuations in ambient electrical or magnetic fields (e.g. Magnetic Anomaly Detection)

There are probably some I’m missing, but this is at least a start. Any given sensor can be active, passive, or both (except chemical, which can only be passive). Passive sensors can only detect objects which emit the appropriate type of energy, or which reflect emissions from other sources. Active sensors emit their own energy and then detect the reflections. Active sensors can be detected from a long way off by passive sensors of the same type (not sure yet what this means in game terms). Active sensors determine range as well as direction, while passive sensors only determine direction unless they use triangulation or some other technique to determine range.

Every character (vehicle or otherwise) with sensors would have a list of the types of sensors they have. For example, a d20 OGL Dwarf would have:

• Optical (passive with distance): two eyes
• Thermal (passive with distance): darkvision
• Acoustic (passive): ears
• Chemical: taste and smell

Other examples: a bat would have acoustic (active), a shark would have electromagnetic (passive), and a spider on its web would have acoustic (passive with distance).

If a particular creature or vehicle has an especially good sensor of one type and an especially bad sensor of another type (e.g. a ship with a great radar but a mediocre sonar), this could be represented by bonuses or penalties to perception checks of that type.

As a corrolary, particular characters could have different DC modifiers against different types of perception, or even be completely invisible to some types of perception (for example, animals are invisible to all but the most high-frequency radars).

[lucasjung]

I've come up with some unified rules for missiles (guided), rockets (unguided missiles), and bombs.

Right now I have rules for speed, range, damage, and weight. I will add another post later with rules for purchase DC and price.

I define all such weapons in terms of their size: a gargantuan missile, rocket, or bomb is one that would be about average among the weapons carried by a gargantuan character; a large missile, rocket, or bomb is one that would be about average among the weapons carried by a large character, etc.

I generated these rules by using a few real-world weapons as benchmarks, nerfed the damage considerably (because real-world weapons are way too lethal for a normal heroic action/adventure game), and fudged some things considerably to fit into the standard progression (1-2-5-etc). The resulting ranges and weights actually turned out pretty good: the weights and ranges are a little high for the smaller weapons and a little low for the larger weapons, but just right in the middle.

A fundamental design goal was to have missiles and rockets with different speeds and ranges, with a trade-off between damage, range, and speed: if you take up more space and weight with propellant (to go faster or further), you have less space and weight remaining for the warhead.

EDIT: Big-time typo for the base range for a standard medium missile (I was short a zero). Also somehow managed to misread the speed for high-speed missiles from e20 Lite 0.5. Both now corrected.
Under my proposed rules, a missile, rocket, or bomb is defined by a number of characteristics:

• Size: Determines weight and standard range. A medium missile or rocket weighs 50 lb, and weight increases one step on the standard progression for every increase in size category. A bomb is one step higher on the progression than a missile of the same size (e.g. a medium bomb weighs 100 lb). The base range for a standard medium missile or rocket is 2000 squares, and range increases one step on the standard progression for every increase in size category. Bombs all have the same range regardless of size, which is discussed later. The minimum size for missiles, rockets, and bombs is Medium. In a sci-fi setting you could make them smaller, but I wanted to focus on modern for now. The base range for standard medium missiles and rockets could also be adjusted for sci-fi settings.
• Type (guided missile, rocket, or bomb): Affects damage. A guided missile does damage in d8s. A rocket (unguided missile) does damage in d10s. A bomb does 4d12 damage (plus size modifiers). A standard missile or rocket does 3 dice of damage (3d8 or 3d10, respectively), but this can be altered by the range and speed of the missile.
• Speed: Affects damage. A regular missile has a speed of 1,000 squares/round (high subsonic). A high-speed missile has a speed of 5,000 squares/round (about Mach 4 at altitude--a pretty typical speed for a modern air-to-air missile). (these are the missile speeds from e20 Lite 0.5, unchanged) A high-speed missile has its number of damage dice reduced by one (2d8 for missiles and 2d10 for rockets).
• Range: Affects damage. A missile or rocket can have extended range (double standard) or reduced range (half standard). An extended range missile has its number of damage dice reduced by one (2d8 for missiles and 2d10 for rockets) while a reduced range missile has its number of dice increased by one (4d8 for missiles and 4d10 for rockets). The effects of altered range and speed stack: a missile or rocket that is both high-speed and extended range does one die of damage (1d8 or 1d10, respectively), while a missile or rocket that is both high-speed and reduced range does three dice of damage (the two modifiers cancel each other out).

EDIT: I completely forgot about area.
EDIT: "One step on standard progression for every two size categories" was akward, so I changed to use the expanded progression.
A medium missile or rocket has area 5 while a medium bomb has area 10. A Large missile or rocket has area 10, and then the area of a missile or rocket increases by one step on the expanded progression for every size category larger than Large. The area of a bomb increases by one step on the standard progression for every size category larger than medium. Here's a brief table:

• Medium: Missile: 5; Rocket: 5; Bomb: 10
• Large: Missile: 10; Rocket: 10; Bomb: 20
• Huge: Missile: 15; Rocket: 15; Bomb: 50
• Gargantuan: Missile: 20; Rocket: 20; Bomb: 100
• Colossal: Missile: 30; Rocket: 30; Bomb: 200
• Extra-Colossal: Missile: 50; Rocket: 50; Bomb: 500

A missile, rocket, or bomb that does splash damage can be given the penetrating trait. If this is done, it is treated as if it were two size categories smaller for purposes of determining its area:

• Medium: Missile: 2; Rocket: 2; Bomb: 2
• Large: Missile: 5; Rocket: 5; Bomb: 5
• Huge: Missile: 5; Rocket: 5; Bomb: 10
• Gargantuan: Missile: 10; Rocket: 10; Bomb: 20
• Colossal: Missile: 15; Rocket: 15; Bomb: 50
• Extra-Colossal: Missile: 20; Rocket: 20; Bomb: 100

EDIT: Considerable revisions to this section because I had the bombs falling way too slowly.
Bomb Range:
I wanted to come up with some rules to make bombs feel appropriately different from other weapons. To that end, I came up with some modified rules for bomb range by breaking up the concept of range into two parts for bombs.

Maximum Range for Bombs:
Unless you're in outer space (or so high up in the atmosphere that re-entry heat becomes a significant factor), there is no limit to how far a bomb can fall: it will fall until it hits the ground. However, there is a limit to how far the bomb can move laterally before it gets to the ground.
When a bomb is released, it will move straight forward in the direction the dropping aircraft was moving at the time of release. Each turn it falls a certain distance and then moves forward a certain distance. Because the bomb falls before moving forward, a bomb will not move forward on the turn that it hits the ground.
On the turn that it is dropped, a bomb will fall a number of squares equal to the dropping aircraft's rate of descent for that turn, rounded up to the nearest step on the standard progression. For example, if the aircraft descended 300 squares that turn, the bomb will drop 500 squares. If the aircraft did not descend at all, the bomb will fall 100 squares. On each subsequent turn, the bomb's rate of fall will increase by one step on the standard progression, up to the bomb's terminal velocity of 1,000 squares per turn.
On the turn that it is dropped, a bomb will move forward at the minimum speed for the dropping aircraft's current speed category. For example, if an aircraft with base speed of 200 squares/round is moving forward at a speed of 500 squares/round when it drops a bomb, it is moving at high speed (more than 2x base speed), so the bomb will move forward 400 squares (2x base speed) in that round. On each subsequent turn, the bomb's forward motion will decrease by one speed category until it reaches zero speed.
In most cases, there is no need to work this out on a turn-by-turn basis: since the initial speed and altitude of the bomb are known, you can immediately figure out when and where it will land, make a note, and then put the bomb out of mind until the turn when it hits.

EDIT: Fixed the range penalties to match the standard progression.
Range Penalties for Bombs:
The range penalty for a bomb is determined by the altitude from which it is dropped:

• Very Low: +0
• Low: -1
• Moderate: -2
• High: -5
• Very High: -10
• Extreme: -20

Note: Much like a grenade, if you miss with a bomb it will hit and explode somewhere, just not where you intended it to. I couldn't find rules for this in e20 Lite 0.5, but bombs would follow the same rules as grenades in this regard (possibly with some modifications).
Note: Rules for guided bombs and glide bombs will come in a later post.

Hardpoints:
I came up with some rules for hardpoints that don't match reality exactly, but which do a reasonably good job of approximating reality while keeping things simple and sticking to the standard progression.

A vehicle with hardpoints can carry one weapon per hardpoint if the weapon is the same size category as the vehicle (e.g. a Gargantuan vehicle can carry 1 gargantuan missile, rocket, or bomb on each hardpoint). For each size category lower the weapons are, the hardpoint can hold a number of weaopns one step higher on the standard progression (e.g. a Gargantuan vehicle can carry 2 huge bombs, 5 large bombs, or 10 medium bombs on each hardpoint). All of the weapons on a particular hardpoint must be identical (e.g. you can't put a bomb and a rocket on the same hardpoint, or even an extended range missile and a standard range missile). If the weapons on a hardpoint are at least two size categories smaller than the vehicle carrying them, those weapons can be used to make barrage attacks.
EDIT: Barrage doesn't make sense mechanically. See my later post for a better idea.

Note: In reality, it is common for aircraft to release many smaller bombs in rapid succession (a "stick" of bombs), or to carry smaller rockets in pods that can fire several in rapid succession. This is not really done with guided missiles; I considered making that a rule, but decided it would be simpler to not include that particular exception.

A vehicle can also carry missiles, rockets, or bombs up to one size category larger on hardpoints (e.g. a gargantuan vehicle could carry colossal bombs). Each such weapon takes up two hardpoints (the weapon isn't really attached to two hardpoints--it's just "crowding out" an adjacent hardpoint so that weapons can't be carried there). Also, a vehicle can only use up to half of its hardpoints (rounded down) to carry over-sized weapons. For example, a gargantuan fighter jet with 9 hardpoints would be able to carry up to 2 colossal bombs on its hardpoints: half of 9 is 4.5, rounded down to 4, with each colossal bomb taking up 2 of those 4 hardpoints.

It might be plausible for a vehicle to carry even larger weapons, but not on hardpoints: they would need dedicated launch mechanisms (such as a truck carrying a mobile ICBM).

Drag:
For purposes of determining aircraft loading, a missile or rocket carried on a hardpoint counts as 1x its actual weight while a bomb counts as 2x its actual weight. A weapon that is of a larger size category than the vehicle carrying it increases this multiplier by one step on the standard progression (i.e. 2x for missiles and rockets, 5x for bombs). Weapons that are at least two size categories smaller also increase this multiplier by one step on the standard progression, representing the bulkier and more complex mounting racks or pods needed to hold so many individual weapons.

Gun Pods:
Any mounted machine gun or autocannon can be purchased in gun-pod form. A gun pod includes 100 rounds of ammunition. The total weight of the gun pod is equal to the weight of the weapon, plus the weight of the ammo carried in the pod, with that sum increased by 10% and rounded up. The size category of the weapon is unchanged. A vehicle can mount a single gun pod of the same size category lower on each hardpoint. Larger gun pods cannot be mounted at all, and only one pod can be mounted on each hardpoint, regardless of how small the gun pod is. The drag multiplier for all gun pods is 2x, regardless of the size of the gun pod.
EDIT: Reloading a gun pod is a complex and time-consuming procedure. First, it has to be removed from the hardpoint it is mounted on (we'll have to figure out reasonable times for loading and unloading weapons to and from hardpoints). Then it has to be opened, reloaded, and closed back up again. This process takes fifty minutes for one person or twenty minutes for two people (adding additional people does not save any further time). Finally, it can be re-mounted on the hardpoint.

Shoulder-fired Missiles:
All bombs, and all missiles and rockets of size Large or larger can only be used as mounted weapons. Medium missiles and rockets can be used as mounted weapons, but heavy versions are also available for sale, representing shoulder-fired missiles and rockets.

[lucasjung]

I looked at the prices for a bunch of real-world bombs, rockets, and missiles, and came up with a unified system for assigning purchase DCs for such weapons. It doesn't match reality perfectly, but it's simple and straightforward.

The purchase DC for a medium bomb is 12.
The purchase DC for a medium rocket is 18.
The purchase DC for a medium missile is 24.

Adding guidance to a bomb increases the purchase DC by +6 (you can't add "guidance" to a rocket--a "guided rocket" is a missile).
Each increase in size category increases the purchase DC by +3.

These increases are cumulative. For example, a gargantuan guided bomb has a purchase DC of 27:
12 (bomb) + 6 (guided) + 3x3 (three size categories larger) = 27

Changing the range or speed of a missile or rocket does not effect purchase DC (the trade-off in damage is more than enough to keep the different speeds and ranges balanced).

EDIT:
A gun in a gun pod has a purchase DC one higher than the regular version of the same gun.

Glide Bombs:
Like a regular bomb, a glide bomb will move straight forward in the direction the dropping aircraft was moving at the time of release, and will descend each turn before moving forward. A glide bomb will descend at a rate of 50 squares per turn, every turn. It will move forward and decelerate like a regular bomb, except that it will stop decelerating when its forward speed reaches 500 squares per turn. If the dropping aircraft is moving less than 500 squares per round when the glide bomb is released, the glide bomb will not accelerate, but instead use the lower speed for its entire descent. If a glide bomb is dropped at a speed less than 200 squares per round, or at a rate of descent greater than 50 squares per round, it will fall out of control just like an out of control airplane and only has a 50% chance of detonating when it hits the ground.

The range penalties for glide bombs are one step higher on the standard progression than the range penalties for regular bombs:

• Very Low: -1
• Low: -2
• Moderate: -5
• High: -10
• Very High: -20
• Extreme: -50

For purposes of mounting on hard points, a glide bomb counts as one size category larger because of the fold-out wings. For example, a gargantuan glide bomb carried by a gargantuan fighter jet will take up two hard points and will have a 5x drag multiplier to its weight.

All glide bombs are guided (because they travel so far, so slowly, they are very susceptible to winds and other influences--an unguided glide bomb would have very little chance of hitting its intended target). A glide bomb has a Purchase DC modifier of +12, which includes the +6 increase for guidance (in other words, it's +6 for wings and +6 for guidance).

I won't bother coming up with rules for guided bombs until I see what Gary has to say about my suggestions regarding weapon guidance in my original post in this thread, and until I know how the miss/scatter rules for grenades and bombs will work.

[lucasjung]

Earlier in this thread, I posted a suggested rule that rockets, bombs, and missiles mounted on hardpoints in clusters of 5 could be used to make barrage attacks. Today it occurred to me that, while this makes sense from a real-world perspective (e.g. ripple-fire rockets or sticks of bombs), it makes absolutely no sense mechanically because barrage is a type of area attack, as are most rockets, bombs, and missiles (blast, splash, or spread). How do you mix the two different types of area attacks? Well, I've decided to answer that question by coming up with a new type of area attack: salvo. A salvo attack is to a blast, splash, or spread attack as a barage attack is to a normal ranged attack.

Salvo:
A salvo attack can only be made with a weapon that does blast, splash, or spread damage. Additionally, it can only be made by a weapon or grouping of weapons capable of launching at least five identical projectiles simultaneously or near-simultaneously from the same point or points in close proximity. Examples of weapons that can make salvo attacks:

• Bombs, rockets, or missiles mounted on a hardpoint of a vehicle at least two size categories larger than the weapons' size category (e.g. a rack of large bombs on a gargantuan fighter, or a pod of medium rockets on a huge helicopter).
• Multiple identical weapons all mounted on the same vehicle, and all capable of aiming at the same target (e.g. turret-mounted naval guns on a ship).
• Multiple identical weapons in close proximity to each other (e.g. a battery of mortars or artillery guns). To qualify as "close proximity" for purposes of salvo fire, each weapon must be within 1/2 space of at least one other weapon. For example, a 60mm Mortar is medium, so it has a space of 1 square, so a group of 60mm Mortars would have to be arranged such that each mortar is adjacent to at least one other mortar. A 155mm Howitzer is XC, so it has a space of 20 squares, so a group of 155mm Howitzers would have to be arranged such that each howitzer is at most 10 squares from at least one other howitzer.

A salvo attack consumes at least 5 rounds. In most cases, it consumes exactly 5. However, if several weapons are mounted together in turrets, not in even multiples of 5, then all of the weapons in each turret must fire. For example, a typical battleship turret holds three 16-inch naval guns. To fire as a salvo, 2 turrets would have to be used (a single turret doesn't meet the requirement of firing 5 projectiles at once). 2 turrets total 6 guns. All six guns have to fire, so 6 rounds would be consumed instead of just 5. To give a counter-example, consider a rocket pod holding 10 rockets. This rocket pod could fire 5 rockets as a single salvo attack, then another 5 later as a second salvo attack. That's because the rocket pod holds a multiple of 5 rockets (10 = 2 x 5). When more than 5 rounds are consumed, the effects are no greater than when 5 rounds are used.

EDIT: I came up with a much simpler way of handling a salvo attack (I deleted the old way):
EDIT: Some of the damage number in the examples were wrong; now fixed.
A salvo attack counts as a single shot from a weapon of the same type, but the area is determined as if it were two size categories larger and the damage is determined as if it were one size category larger. For example, a salvo attack made with five large bombs (4d12+2 damage each, area 20) would instead count as a single gargantuan bomb (4d12+5, area 100). This may not sound like a good tradeoff if you add up the damage from those five large bombs and realize that they could do 30-250 damage (way more than 4d12+5), but it actually is a good deal in certain circumstances, mostly against dispersed targets.

[lucasjung]

I decided to flesh out my ideas for guided weapons into a full set of rules. These rules are for self-propelled guided weapons (missiles, torpedoes, etc.). Rules for guided bombs will come later.

A guided weapon has an Intelligence score to indicate how effective the guidance mechanism is. All checks involving guided weapons use the appropriate skill of the attacking character, but do not use any of the attacking character's ability scores, instead substituting the weapon's Intelligence bonus in all cases.

Guided weapons can behave somewhat differently depending on whether the range to the target is less than the weapon's speed (in other words, whether the weapon will hit the target in the same turn that it was fired).

Target Lock:
Regardless of the range to the target, the attacking character must acquire a target lock before firing a guided weapon. Acquiring a target lock is a swift action (Sense vs. Reflex). If a guided weapon depends on cueing from an electronic sensor (radar, FLIR, etc), Computers is used for Sense; if the weapon is aimed manually (e.g. shoulder-fired missile), Perception is used. Range penalties apply to the check to acquire a target lock. If the weapon is not fired, the target lock is lost at the end of the character's turn and a new lock must be acquired before the weapon can be fired

Range to Target is Less than or Equal to Weapon's Speed:
In this situation, the weapon will reach the target in the same round that it was fired. After the target lock is acquired, the weapon can be fired as a standard action and the attack roll is made immediately. The attack roll is considered to be made at point-blank range so no range modifiers apply. If the attack misses, the missile is lost and cannot make any more attack rolls.
In this situation, the attacker can also choose to disengage the weapon's guidance systems before firing. In this case, no target lock is required and the attack roll is made as if the weapon were unguided (i.e. the attacker's ability modifiers are used and range penalties apply).

Range to Target is Greater than Weapon's Speed:
In this situation, the weapon will take more than one turn to reach the target. The attack roll is not made when the weapon is fired, but rather when the weapon reaches the target. Firing the weapon is considered a ranged attack and uses a standard action even though no attack roll is made. When the weapon is fired, it immediately moves a number of squares equal to its speed directly towards the target.

On each subsequent round, the guided weapon moves a number of squares equal to its speed directly towards the target. This move happens at the end of the target's turn on every round after the round when the weapon was fired. If the weapon enters the same square as the target, it immediately stops moving and makes an attack roll against the target's Primary Defense. The attack roll is considered to be made at point-blank range so no range modifiers apply. If the attack misses, the missile is lost and cannot make any more attack rolls.

As a move action, the target can try to break the weapon's lock by making an opposed check, using either Control (Dex) or Stealth (Int) vs. Sense. Range penalties apply to this check in different ways depending on the circumstances. If the target is attempting to break lock using Control, a penalty based on the distance between the weapon and the target is applied against the target and a penalty based on the speed of the target is applied against the weapon. If the target is attempting to break lock using Stealth, a penalty based on the distance between the weapon and the target is applied against the weapon and a penalty based on the speed of the target is applied against the target. If the check is a tie, the lock is not broken. If the lock is broken, the weapon is lost and cannot re-acquire the target. If a target successfully breaks lock against a group of missiles fired as a salvo, it only breaks lock against some of the missiles, with others still locked on to the target. This is represented in game terms as follows:

• After the first successful broken lock, the salvo acts as a single guided weapon of one size category larger than the constituent weapons (as opposed to two size categories).
• After the second successful broken lock, only one of the constituent weapons is still locked on. The weapon is no longer considered a salvo and is instead treated like a normal individual weapon of the type fired.
• A third successful broken lock will eliminate the final remaining weapon.

[lucasjung]

Most attacks that do Burst, Splash, or Spread damage will still have some sort of effect even if they miss. Such an attack might not damage the intended target(s), but it's going to land somewhere and if it goes off anything sufficiently close to that point is going to get hit. For example, if you throw a grenade or drop a bomb, it's going to explode no matter what, it just might not explode where you wanted it to. There are, however, weapons that won't do this. For example, most surface-to-air and air-to-air missiles have sophisticated fuses which prevent them from exploding unless they are close enough to the intended target to do damage.

I mentioned earlier that I couldn't find rules for scatter in e20 Lite 0.5. I finally realized that this phenomenon is modeled in the rules for area weapons, just in a more abstract way than I am used to: each type of area attack has rules for lesser damage on a hit by five or less. That works well enough when the only potential target in the vicinity is the intended target. It is also perfect for weapons with proximity fuses like I mentioned in the previous paragraph. However, if there are other nearby enemies (or allies, or bystanders), the potential for collateral damage exists. The existing rules don't model collateral damage, so I'm going to off a suggestion for scatter rules to be used for area weapons in situations where a miss against one target might turn into a hit against a different target. GMs would then be able to decide which mechanic (abstract or scatter) fits best in any given situation.

I wanted to come up with rules that assign the direction of miss randomly (easy), and that determine miss distance based on the range from the target to the attacker and the difference between the roll and the target's defense (much harder to balance well). Here's what I came up with:

Miss Direction:
Since e20 uses a square grid with diagonal movement allowed, there are eight possible directions for a missed attack to go (four cardinal directions plus for diagonals). To determine the direction, roll a d8. On a roll of 1, the weapon continues in the direction it was traveling (i.e. it overshoots); for each number higher than 1, the miss direction moves 45 degrees clockwise:

8 1 2
\ | /
7- -3
/ | \
6 5 4

Miss Distance:
The miss distance is equal to the sum of the range penalty for the attack, half the area of the weapon (rounded down), and the margin of failure. For example, a 105mm Howitzer makes an attack at a target at a range of 2,000 squares, making the range penalty 5 (medium range). The total attack roll is 18 against a defense of 25, so the attack misses by 7. A 105mm Howitzer has an area of 10 squares. The attack misses by 5 + 10/2 + 7 = 17 squares.

The maximum miss distance is equal to one-half the maximum distnace for the range increment of the attack. For example, a grenade has a range of 2, so the maximum distance for a long-range attack with a grenade is 2x10 = 20, making the maximum miss distance 20/2 = 10. If a grenade is thrown at target at long range (range penalty 10), with a total attack roll of 12 against a defense of 19 the attack misses by 7. A grenade has an area of 5, so according to the formula it would miss by 5 + 5/2 + 7 = 14. However, the maximum miss distance for a grenade at long range is 10, so the grenade only misses by 10. This limitation does not apply on a natural roll of 1 (so that it is possible to drop the grenade at your own feet).

[lucasjung]

I came up with some proposed rules for fuel consumption. In a heroic game, tracking fuel consumption is an undesireable distraction, so these would be alternate rules for use in "heroic realism" or "gritty realism" games.

This system is a little math-heavy, and so is not intended to be used on the fly. Instead, a fuel-consumption table should be generated for a vehicle before it is used so that fuel use can be looked up quickly.

A vehicle that is moving consumes fuel every round equal the maximum speed for its current speed category divided by 10 and squared, multiplied by its size multiplier. For example, a jet fighter (gargantuan, so size multiplier 5) moving at high speed (up to 1,000 squares/round) would use (1000/10)^2 x 5 = 50,000 units of fuel every round. A compact car (large, so size multiplier 1.5) moving at high speed (up to 40 squares/round) would use (40/10)^2 x 1.5 = 24 units of fuel every round. Fuel consumption is based on the number of movement points used, not the number of squares actually traveled, so that a climbing aircraft will use more fuel and a descending aircraft will use less. Other actions can cause a vehicle to consume additional fuel:

• Hard Turn: A hard turn naturally causes a vehicle to decelerate, so extra fuel is required to maintain speed through a hard turn. When a vehicle makes a hard turn, it consumes additional fuel equal to the maximum speed for its current speed category divided by ten, multiplied by its base speed, multiplied by its size multiplier.
• Change Declared Speed: If used to decelerate, this manuever does not consume any additional fuel. When a vehicle uses this manuever to accelerate, it consumes additional fuel equal to the maximum speed for its current speed category divided by ten, multiplied by its base speed, multiplied by its size multiplier, multiplied by two for an increase of one speed category; or the maximum speed for its current speed category divided by ten, multiplied by its base speed, multiplied by its size multiplier, multiplied by five for an increase of two speed categories.
• Exceed Maximum Speed: When a vehicle performs this manuever, it consumes additional fuel equal to the the amount of fuel it would normally consume by moving at maximum speed for one round.

Fuel Weight:
Fuel is measured in pounds (since all other vehicle loadings are measured in pounds, this keeps things consistent--plus, it's how most aircraft measure fuel in the real world). One pound of fuel is worth 5,000 units of fuel.

Note:
If you were to do all the math and figure out the miles/gallon (for a car) or the pounds/hour (for a jet), you would see that this only does a marginal job of matching reality. However, I tried many different formulas. This was the simplest system which worked for both fighter jets and cars, without being obscenely complex. It's definitely complex, which is why I set it up so that the math can all be done ahead of time, but it's not nearly as complex as some of the other things I tried in an attempt to get the numbers closer to reality.

[GMRob]

One quick thought posted from my phone: Give the missiles a Will Defense, to reduce opposed rolls for breaking Target Lock. Just an idea.

[lucasjung]

One quick thought posted from my phone: Give the missiles a Will Defense, to reduce opposed rolls for breaking Target Lock. Just an idea.

I had actually considered that, but the feedback I get usually indicates that I'm making things more complex than they should be, so I've been trying to err on the side of simplicity. However, since you suggested it, I'll go ahead and second you. We could also maybe give them a Wisdom score to use for Sense checks, instead of using Int for sense checks. We'll see what Gary thinks. I'm guessing that he'll ixnay the whole idea of giving guided weapons ability scores of their own and stick to his original idea of having them simply provide a bonus to the operator. I'm just hoping that some of the stuff I throw out here proves useful to some degree or another. Thanks for the feedback!

[GMRob]

I wouldn't be surprised if that ends up being the case as well, but if not, assigning a Will def based on the quality of the guidance system seems a lot easier to me than giving them ability scores and making skill checks.

[lucasjung]

Something just occurred to me:

On table 8-10, the Fort Defenses for the aircraft generally seem too high. Also, some of them are out of whack in relation to each other: a fighter jet should should not have higher MDT than an attack helicopter. Even worse, the jet airliner and jumbo jet have higher MDT than the combat aircraft, almost as high as a tank! To me, MDT can represent different things for different types of vehicles. For something like a tank, it represents pure toughness. For something more fragile like an aircraft, it might represent some of that (such as a well-armored attack helicotper), but mostly it represents survivability features like redundant, separated systems, or self-sealing fuel tanks with baffles. Non-military aircraft have redundant systems (which protect against failure and malfunction) but not separated redundant systems (which also protect against damage). For example, both military and civilian aircraft have multiple hydraulic systems for moving the flight control surfaces. If one system fails, the others allow the pilot(s) to continue controlling the aircraft. However, on military aircraft these systems are also separated: the hydraulic lines run different routes through the aircraft, so that a hit in one place will only take out one hyrdaulic system instead of all of them. Such separation is usually not designed into commercial aircraft, so that a single hit in one place could easily take out all of the redundant systems at once. Self-sealing fuel tanks with baffles are another big one: non-self sealing tanks almost inevitably lead to catastrophic fire when shot. Tanks without baffles are also subject to hydrostatic shock when shot: even a single round of small arms fire will cause the tank to burst with sufficient force to literally tear an entire wing off of a plane (since the main tanks are typically located in the wings). About the only thing that the big passenger jets have going for them are lots of engines, but most military aircraft also have multiple engines, with any single engine providing sufficient thrust to limp home safely.

[lucasjung]

Rules for submarines were not included in e20 Lite 0.5, so I came up with some.

Before I get to that, however, I have realized that the Gunnery skill needs two additional specializations:

• Bombs: Includes aerial bombs (like the ones I posted rules for above) as well as depth charges (just the basic kind; hedgehogs, squids, and other depth-charge mortars would fall under the mortars & artillery specialization while rocket-propelled depth charges would fall under the rockets & missiles specialization).
• Torpedoes: Self-explanatory.

OK, now on to my proposed submarine rules:

To start with, I'm going to discuss a few background concepts:

Visibility and light penetration:
When you stand at the end of a pier and look down into the water, you can see a certain depth down, after which everything gets too dark to see. If you've ever looked down into water from a tower or plane, you may have noticed that you can see things quite a bit deeper than if you were standing just above the water. If you get too high, however, you can't see past the surface of the water at all. This effect, of being able to see deeper, then not at all, as you increase in elevation, happens because of the way water and air reflect and refract light. I'm not real keen on the details, so don't ask.

If you go under the water, the deeper you go, the darker it gets. That's because light is absorbed by water and by particles suspended in the water, and the deeper you go the more water and particles there are between you and the surface to absorb light. When you get deep enough, there isn't enough light to support photosynthesis, so plants can no longer survive. This is known as the aphotic zone.

The effects discussed above vary significantly depending on the type of water (fresh or salt) and how clear or murky it is. In the rules that follow, I've based everything on open ocean. If you're dealing with water murkier than that (such as a muddy lake or estuary), visibility and light penetration will be worse. If you're dealing with clearer water (such as a pristine mountain lake), visibility and light penetration will be better.

Thermocline:
As you go deeper into water, it generally gets colder. The thermocline is a layer in the ocean (or in a large lake) where the rate of temperature reduction with depth is significantly higher than in the water above and below. The thermocline can move a lot. In the tropics it's almost always from about 300 feet to about 600 feet. In temperate areas it can get as deep as 3,500 feet, usually in the summer. In the arctic, it usually doesn't exist (the water at the surface is already about as cold as it can get).

The thermocline is important to these rules because it creates a negative sound speed gradient, which reflects and refracts sound waves, making it nearly impossible to use sonar effectively to find things on the opposite side of the thermocline. Submarines can "hide" from ships by going below the thermocline. Of course, they're not hidden from other submarines that are also below the thermocline.

Modern vs. WWII subs and torpedoes:
Submarines didn't change a whole lot from WWI to WWII. They changed dramatically in the post-war years. In WWII and before, a submarine was really a boat that could go underwater for a while in order to escape more heavily armed ships. They spent most of their time on the surface and were optimized more for the surface than for underwater: they couldn't go as fast underwater as they could on the surface. Modern submarines are the opposite. Modern submarines generally only surface to enter and exit port and are completely optimized for movement underwater: they go faster underwater than they can on the surface.

Torpedoes changed significantly after WWII because of the advent of guided torpedoes: modern torpedoes are all guided (except for some crazy experimental super-speed underwater rockets like the one that blew up the Kursk). For a missile, the guidance system represents a significant portion of the missile's weight, and weight is always a critical consideration for something that flies through the air, so it still makes sense in some cases to make unguided rockets. Not so with torpedoes: they are already so large and heavy that the guidance system doesn't represent as big a percentage of the total, and while mass is still important, it's not as critical as it is with aerial missiles, so there's no significant advantage in leaving the guidance system out. In addition to changing torpedo tactics (longer-range shots are feasible with guidance, and big spreads of torpedoes are no longer needed), guidance allowed torpedoes to become an anti-submarine weapon. A WWII torpedo would only work against a submarine if that submarine happened to be surfaced at the time. WWII submarines were pretty much useless for hunting other submarines. A modern guided torpedo can attack a submarine at any depth, and submarines are now the best weapon for hunting other submarines. One other thing changed significantly about torpedoes: the way they cause damage. A WWII torpedo had a contact fuse in the tip and would literally ram a ship just below the waterline, then explode there. This was generally more effective than guns at sinking ships because it created a big hole below the waterline. Modern torpedoes take it to an entirely different level: they use a proximity fuse to explode underneath the ship. The explosion creates a huge bubble of gas under the water, pushing up on the center of the keel and stressing it. Then, the bubble collapses, leaving the center of the keel unsupported by water. The target ship literally snaps in half. Needless to say, I will be nerfing the damage for torpedoes considerably in order to keep things within the scope of "heroic adventure."

Airplanes, Submarines, and Submersibles:
Like airplanes, submarines can move in three dimensions. Actually, it's not very much "like airplanes" at all. Both aircraft and submarines have forces acting on them to push them up, and other forces acting to push them down. They control their altitude or depth by manipulating the balance between these forces. For aircraft, the main downward force is weight and the main upward force is lift. Submarines and submersibles use ballast to make the overall density of the sub about the same as the density of the surrounding water, rendering the sub "neutrally bouyant." A "neutrally bouyant" object in the water will tend to stay at its current depth, neither rising (as a less-dense object would) nor sinking (as a more-dense object would). Subs aren't generally perfectly neutrally bouyant, but they are close enough that the rate of sinking/rising is small enough to be controlled by other means. Where an aircraft needs to manipulate its lift to be in equilibrium with its weight for level flight (or out of equilibrium to climb or descend), a sub is generally always in equilibrium and must introduce other forces to change its depth.

A modern military submarine uses planes (the bits that look like stubby little wings on the sides of the conning tower or the sides of the bow) to change the attitude of the submarine, pointing it up or down. This changes the thrust vector from the screws so that a component of the thrust is either pushing the sub up or pushing it down, with the majority of the thrust continuing to push the sub forward. Because the planes only work if there is water flowing past them, and because the change in depth is achieved through thrust from the screws, and because there are practical limits to how far up or down a submarine can tilt its bow, a submarine must be moving forward in order to change depth and the ratio of depth change to forward movement is limited. Also, most modern submarines, when submerged, have slightly negative neutral bouyancy, which is offset by small amounts of lift generated when the submarine is in forward motion. For this reason, a submarine that stops moving will start to sink slowly. Very little forward motion is needed to prevent this. Because they control their direction using rudders, which only work when water is flowing past them, submarines also can't control their direction unless they are moving forward.

Most research submersibles (such as Alvin), behave very differently from submarines. They have many different propellers and/or impellers pointed in various directions to provide significantly more agility. They can turn in place, move straight up and down, side-to-side, etc.

All types of submarines and submersibles generally have the ability to purge their ballast in an emergency, which causes them to rise rapidly to the surface. This is a brute-force technique and can't be used half-way: you can't purge your ballast to rise straight up for a round or two, then pump new ballast back in to halt the ascent. Once the ballast is purged, the sub is going all of the way to the surface.

I tried to make depth rules that were similar to the altitude rules, but my main priority was to make them feel right.

Nuclear Weapons and Power:
You can't talk about modern submarines without talking about nuclear power and nuclear weapons. Before I say anything else about this, I want to start by clearing up a common misunderstanding: the term "nuclear submarine" refers to a submarine that is powered by one or more nuclear reactors. A nuclear submarine might or might not carry nuclear weapons. In fact, the first submarines to carry nuclear weapons predated nuclear submarines: there were diesel-electric submarines that carried nuclear-armed cruise missiles. As far as I know, all modern nuclear-armed submarines are also nuclear powered. A modern nuclear-armed submarine is called a "ballistic missile submarine" or SSBN.

There are huge advantages to nuclear power: a nuclear submarine can stay submerged indefinitely (this is probably the single biggest advantage, because submarines rely on stealth for survival), can move significantly faster than a diesel-electric submarine, and is quieter than a submarine running on diesel. However, even today diesel-electric submarines are still being built. There are a few reasons for this: first and foremost, not every nation has access to compact reactor technology; second, diesel-electric subs are much cheaper to build and maintain than nuclear submarines; third, when operating on batteries with the diesel engines off, they are somewhat quieter than nuclear submarines. There are some rather impressive recent advances in "air independent propulsion" which allow modern diesel-electric submarines to operate for longer periods of time without their snorkels, but ultimately they still need to snorkel most of the time.

I dabbled with the idea of making up rules for nuclear weapons, but concluded that nuclear weapons should always be handled cinematically. If you're anywhere near a nuclear blast, you're toast ("Roll a reflex save for half damage, DC 1,000. Oh, wait. Even half damage would vaporize you five times over. Go ahead and put down the d20 and pick up some d6s: it's time to roll new characters!"). If nuclear weapons are employed in a game, the characters are either far enough away to be completely safe, or on the periphery where effects are minimal. In either case, a cinematic description by the GM is the most appropriate was to model a nuclear explosion. In the latter case, the GM might want to throw in some minor effects (checks to avoid being blown down, damage from flying debris, etc.), possibly even a skill challenge to get to safety before the fallout starts settling. If you're thinking about using a nuclear explosion in your game, check out Ground Zero, a tool that projects nuclear blast areas on Google Maps.

All that being said, I did need to come up with some stats for nuclear missiles to include on the ballistic missile submarine (not stats for the warhead, just for the missile). A modern nuclear warhead is remarkably small and light, so I reasoned that any nuclear missile (ballistic or otherwise) would be both high-speed and extended-range: the limited remaining space and weight would be more than enough for a nuclear warhead. I checked wikipedia and found that a Trident II (the missiles currently carried on U.S. subs) weighs about 130,000 lbs and has a range of about 7,000 miles; a Minuteman III (the land-based missiles currently in U.S. silos) weighs about 80,000 lbs and has a range of about 8,000 miles. Under my proposed missile rules, a 6XC high-speed extended-range missile would weigh 100,000 lbs and have a range of ten million squares (just over 8,000 miles). I thought I would have to do some fudging, but the rules I set up scale pretty much perfectly! So, there you have it: an intercontinental ballistic missile would be, in game terms, a 6XC high-speed extended-range missile.

Limits on Time Submerged:
Vehicles and equipment designed to carry oxygen-breathers underwater are limited in how long they can stay underwater. Different types of vehicles are generally limited by different constraints:

• Dive gear is generally limited by the size of the oxygen supply. I don't know much about scuba gear, rebreathers, mixed-gas rigs, etc. Hopefully someone who does can provide some stats for such gear, including how long they last.
• Research submersibles are typically powered entirely by electricity, and carry a finite supply of stored oxygen for breathing. The battery and oxygen stores are generally designed so that both would run out at about the same time (in other words, neither is a definitive limiting factor). Typically they're good for a few hours.
• Modern diesel-electric submarines are capable of producing their own oxygen for breathing, so their time submerged is limited by power supply, not oxygen supply. With their snorkels up, they are limited by the amount of fuel they carry (a length of time most likely measured in weeks). With their snorkels down, they are limited by the amount of electrical power they can store in their batteries (a length of time measured in hours, maybe a few days; submarines with air independent propulsion can stay submerged for two or three weeks).
• Like diesel-electric submarines, nuclear submarines are capable of producing their own oxygen. They never need to surface or use a snorkel for purposes of producing power. They are limited in their time submerged by the amount of food they can carry for their crew (a length of time measured in months).

Enough backround...on to the (proposed) rules!

Movement and Depth:
When an underwater character changes depth by one square, it counts as one square of movement, so that an underwater character's total speed for a round is the number of squares moved forward plus the number of squares moved up and down.

An underwater character with limited movement can move one square up or down for every two squares moved forward. An underwater character with limited movement that does not move forward at least its space in squares each round cannot turn, cannot move up, and sinks at a rate of one square per round.

Like flying characters, an underwater character with limited movement can have the hover trait. An underwater character with the hover trait can turn in place, can move backwards, can sideslip, and can move up or down irrespective of the number of squares moved forward. An underwater character with the hover trait does not automatically start sinking when it moves less than its space in squares.

Speed:
The listed base speed for a vehicle designed for underwater movement (e.g. submarine or submersible) is its base speed when submerged. When such a vehicle is on the surface, its base speed is halved (rounded down, minimum 1). This that means its maximum speed is also halved, as are all of its speed categories. For WWII or earlier military submarines, this relationship would be reversed (listed base speed is surface speed, submerged speeds are halved). A submarine with its persiscope or snorkel up uses whichever speed is worse (in other words, a modern sub with its periscope or snorkel up has speeds as if it were surfaced, while a WWII or older sub with its periscope or snorkel up has speeds as if it were submerged).

Depth Levels:

• Near-Surface: Down to 10 squares (50 ft). Objects at this depth level are visible to observers above the water. Most humans cannot go below this level without an air supply (in fact, most humans can't even get near the bottom of this level without an air supply). Submarines must be at this level to use their periscopes or snorkels.
• Very Shallow: Down to 20 squares (100 ft). Objects at this depth level are visible to observers at low or moderate altitude. Scuba divers do not generally go below this level.
• Shallow: Down to 50 squares (250 ft). Objects at this depth level are visible to observers at moderate altitude. Scuba divers need extra oxygen to go to this level and the risk of decompression sickness is significantly increased.
• Moderate: Down to 100 squares (500 ft). Objects at this depth and below are not visible from above the water. Light from the surface is noticeably reduced at this level. Divers with ordinary scuba gear cannot descend to this level; instead, special mixed-gas supplies are needed.
• Deep: Down to 200 squares (1,000 ft). Light from the surface is significantly reduced at this level. Only saturation divers can dive this deep.
• Very Deep: Down to 500 squares (2,500 ft). Very little light from the surface reaches this level, but photosynthesis is still possible. Divers cannot go this deep: humans need a pressure hull to survive at this level or below. This is the deepest level that military submarines can reach.
• Extreme: Everything below 500 squares (2,500 ft). Less than 1% of light from the surface reaches this deep, and photosynthesis is impossible. Only specially designed research submersibles such as the Alvin or the bathyscape Trieste, or robotic submersibles (usually used for resource extraction) can go this deep.
• Thermocline: This isn't a depth level, it's a layer which separates two particular depth levels. At the beginning of any underwater encounter, the GM should announce the location of the thermocline for that encounter. The DC is increased by +10 for all Sense (acoustic) checks against objects or characters on the opposite side of the thermocline. In the tropics, the thermocline should always be between the shallow and moderate depth levels. In the arctic, there should never be a thermocline. In temperate ocean waters, the thermocline should vary with season: between shallow and moderate in the winter, between moderate and deep in spring and fall, and between deep and very deep in the summer. Very large and deep lakes (such as the great lakes) should have thermoclines, but smaller lakes should not. The location of the thermocline is ultimately at the GM's discretion, but should never change over the course of a single encounter.

An underwater character which sinks delow its maximum depth takes crushing damage at the beginning of its turn every round. The amount of damage depends on the size of the character and the number of depth levels below its maximum. The damage one depth level below maximum is 2d12, plus additional damage as if the weapon were of the same size category as the character. For every additional depth level below its maximum depth, the number of dice increase by one step on the standard progression. For example, a colossal submarine one depth level below its maximum would take 2d12 + 30 damage each round, while a huge submersible two depth levels below its maximum would take 5d12 + 4 damage each round.

Loss of Control:
An uncontrolled underwater vehicle behaves like a regular uncontrolled vehcile, with one additional effect: depth change. If the vehicle positively bouyant (e.g. a submarine which has purged its ballast) it rises towards the surface at a rate of one depth level per round. Otherwise, it sinks at a rate of one square per round (even if it has the hover trait).

Decompression Sickness:
A non-water breathing creature (e.g. a human) who ascends from depth too rapidly risks decompression sickness. This does not apply to characters inside pressure hulls (e.g. submarines). Each time such a character changes to a higher depth level, he must wait at the bottom of the new depth level for a period of time (see table, below for times) or make a Fort Save (DC = 15 + skipped time in minutes). On a successful save, no decompression sickness effects occur; on a failure, the character suffers constitution damage (see table, below for damage) which can only be cured by treatment in a hyperbaric chamber for 5 hours. Whether the save is successful or not, any time skipped is added to the required wait time at the next depth level (cumulative). On a successful save, the damage for a failed save at the next depth level is increased by one dice category (cumulative).
Table:

• From Deep to Moderate: Wait time: 20 minutes; Damage: 1d10
• From Moderate to Shallow: Wait time: 10 minutes; Damage: 1d8
• From Shallow to Very Shallow: Wait time: 5 minutes; Damage: 1d6
• From Very Shallow to Near-Surface: Wait time: 2 minutes; Damage: 1d4

Examples:

• A scuba diver at shallow depth forgets to make a decompression stops when ascending to the surface. When ascending from shallow to very shallow depth, the skipped time is 5 minutes, making the Fort Save DC 20. He fails the save and takes 1d6 Con damage. When ascending from very shallow to near-surface depth, the skipped time is 7 minutes (5 carried over, plus 2 more), making the Fort Save DC 22. He fails the save again and takes an additional 1d4 Con damage.
• A diver on mixed gasses is running low on breathing gas and doesn't have enough left to wait for the full amount of time at each decompression stop. When ascending from moderate to shallow depth, he only stops for 7 minutes, so he skipped 3 minutes, making the Fort Save DC 18. He succeeds at the save, but the 3 minutes carry over to his next decompression stop and the damage if he fails at the next stop is raised from 1d6 to 1d8. When ascending from shallow to very shallow depth he only stops for 4 minutes, so he skipped 4 minutes (1 from this stop, 3 carried over), making the Fort Save DC 19. He succeeds again, but the 4 minutes carry over and the damage at the next stop is raised from 1d4 to 1d8 (he has now made two saves, to it increases by two damage dice). When he ascends from very shallow to near-surface depth, he only waits 2 minutes, so he skipped 4 minutes (all of it carried over), making the Fort Save DC 19. This time he fails, and so takes 1d8 Con damage.

new Manuevers:

EDIT: Just remembered that there are no full-round actions in e20. Changed Emergency Surface to comply.

• Steep Dive or Ascent (Dex, limited only): An underwater character with limited movement can climb or descend more steeply than normally allowed. At the beginning of a move action, make a control (Dex) check against DC 20. On a success, you can move one square of depth for every one square of forward movement (instead of every two squares of forward movement) for the remainder of this move action. On a failure by 5 or more, your vehicle becomes uncontrolled.
• Emergency Surface: As a standard action, an underwater character with ballast can surface rapidly by ejecting the ballast (e.g. a submarine purging its ballast tanks or a diver dropping his weighted belt). The character rises one depth level per round and cannot take any other actions until one round after it reaches the surface. The character continues moving forward in the last direction it was moving, but its speed is reduced by one speed category each round. A character subject to decompression sickness must roll all Fort Saves as normal.

Power and Oxygen:
A nuclear submarine can stay submerged indefinitely. A diesel-electric submarine can stay submerged indefinitely as long as its snorkel is up and working. A diesel-electric submarine with its snorkel down can stay submerged for one day before it must surface or use its snorkel. A battery-powered research submersible can operate for a finite number of hours defined in its statistics.

Weapons:

Torpedoes:
My proposed rules for torpedoes are similar to my proposed rules for rockets and missiles, but with much less variation. All modern torpedoes are guided (all WWII and earlier torpedoes are unguided). All modern torpedoes move at a speed of 100 squares/round. All torpedoes do 4d12 splash damage (plus size modifiers). A torpedo that is the same size category as the target or larger is treated as if it has the devastating trait. All modern torpedoes have the penetrating trait (WWII and earlier torpedoes do not). The smallest torpedo size is Gargantuan. A Gargantuan torpedo has a base range of 500 squares and the range increases by three steps on the expanded progression for each size category larger than Gargantuan. A Gargantuan torpedo has area 10, and the area increases by one step on the expanded progression for every size category larger than Gargantuan. A Gargantuan torpedo weighs 750 lbs and the weight increases by four steps on the expanded progression for each size category larger than Gargantuan. The purchase DC for a Gargantuan torpedo is 35 and the purchase DC increases by 3 for every size category larger than Gargantuan. Just like missiles and rockets, ranges and speeds should be decreased for historical settings and increased for sci-fi settings, with torpedoes smaller than Gargantuan being possible in sci-fi settings. A torpedo tube is designed to fire torpedoes of a particular size, and cannot fire torpedoes of larger or smaller size categories.

Aircraft can carry torpedoes on hardpoints using the same rules as missiles or bombs, except that they can't carry torpedoes of a larger size category on hardpoints (a specially designed aircraft could carry larger torpedoes inside a bomb bay, however). Torpedoes have a drag multiplier of x2 to weight. Torpedoes must be dropped from low altitude or below, at low speed or below; if dropped from higher altitude or speed than this, they are destroyed upon impact with the water. An aircraft cannot obtain a target lock on a submerged target, so slightly different rules apply for guided torpedoes dropped from aircraft. First, the torpedo must be programmed to a particular depth level (or to the surface) before it is dropped. Once it enters the water, it begins circling and descending: each round, it moves forward at its speed, turns 45 degrees counter-clockwise, and descends one depth level. Before each of these movments (forward, turn, descend) and after the last, it makes a Sense (acoustic) check against any vehicles within its remaining range, out to 45 degrees either side of its nose, at its current depth level and the depth levels immediately above and below. The first time it successfully detects a vehicle, it establishes a target lock on that vehicle and begins pursuing it using the rules for guided weapons I proposed above (if it was programmed to the surface it will ignore targets below the surface, and vice-versa).

Archaic (unguided) torpedoes:
My proposed rules are primarily focused on modern (guided) torpedoes, but employment of archaic (unguided) torpedoes was so different that I wanted to provide rules for using them. Since they were unguided, and because they took significant time to travel to their targets, it was possible to evade archaic torpedoes by maneuvering to not be where they were aimed. Torpedo boats, destroyers, and submarines compensated for this by firing several torpedoes at a time, aimed to fan out in a wedge as they traveled: a spread of torpedoes. A ship or submarine with multiple torpedo tubes can make a spread attack by firing more than one torpedo at a time, with the only limit on the number of torpedoes being the nmber of loaded tubes capable of aiming at the target (e.g. a submarine with eight bow tubes and four stern tubes could fire all eight bow tubes at once). The attacker must choose a target square when firing. The center torpedo in the spread will always move directly towards this target square each round (if an even number of torpedoes are fired, the attacker designates one of the two center torpedoes as the center torpedo). The other torpedoes start in the same square as the center torpedo, moving in the same direction. After every 10 squares of forward movement, the other torpedoes each slide outward to create the spread effect: the torpedoes on either side slide one square away from the center torpedo, perpendicular to the direction of travel; the next pair of torpedoes out each slide two squares away from the center torpedo, etc. If a torpedo enters the same square as a ship, an attack roll is made for that torpedo.

Archaic torpedoes dropped from aircraft could not be fired in spreads, since each aircraft typically carried only one. Instead, they would travel in a straight line along the same direction the aircraft was flying when it dropped them.

Torpedo Missiles:
This is a missile which carries a guided torpedo instead of a standard warhead. A particular square is targeted, and when the missile reaches that square it releases the torpedo into the water. Firing this type of weapon requires both Gunnery (Missiles & Rockets) and Gunnery (Torpedoes). Instead of a target lock, a Gunnery (Missiles & Rockets, Int) check is made to program the missile to go to the desired square, which is a swift action. When the missile gets to the target square, the torpedo is released into the water and follows the rules for a guided torpedo dropped by an aircraft. A torpedo missile carries a torpedo one size category smaller (e.g. a Colossal torpedo missile carries a Gargantuan torpedo). All torpedo missiles are considered reduced range and standard speed. A torpedo missile has a purchase DC equal to the purchase DC of the torpedo +2.

Submarine Missiles:
Submarines can carry and fire missiles in a number of ways:

• Vertical Launch Tubes: A submarine can have vertical launch tubes designed for missiles of a particular size. These tubes cannot hold missiles of larger or smaller sizes, only the exact size they are designed for. These tubes can be fired at the Deep depth level or less, and can be fired with the submarine surfaced. They can only be reloaded at the pier, or when moored alongside a submarine tender in calm waters.
• Mast-mounted Launchers: Medium-size missiles can be mounted in a launcher mounted on a mast (alongside the periscope and radar). These launchers can only be fired with the periscope up (Near-Surface depth level) or with the submarine surfaced. These launchers can only be reloaded at the pier, or when moored alongside a submarine tender in calm waters.
• Torpedo Tube Capsules: Missiles can be enclosed in special capsules which allow them to be fired from torpedo tubes intended for torpedoes of the same size category. For example, a Gargantuan missile could be loaded into a torpedo tube capsule and then fired from a tube designed for Gargantuan torpedoes. These missiles can be fired at the Moderate depth level or less, but not with the submarine surfaced. The missiles can only be encapsulated at land-based facilities, but pre-encapsulated missiles can be loaded into torpedo tubes by the crew within the submarine. Encapsulating a missile increases the purchase DC by one.

Depth Charges (basic):
These are archaic weapons, no longer in use because they have been completely supplanted by guided torpedoes. This category encompasses barrel-style depth charges rolled off of stern racks on ships, as well as depth bombs dropped by aircraft. Ships stopped carrying depth charges of this type shortly after WWII, but aircraft continued utilizing them at least into the late 1960s.

A basic depth charge weighs the same as a bomb of the same size and does 4d12 blast damage with the same area as a torpedo of the same size. Before an attack is made with a depth charge, the attacker must announce the depth level where it will explode. If the target is not actually at that depth level, the attack automatically misses (although GMs should still have the attack make an attack roll, to avoid revealing the actual depth level of the target). Range penalties are based on the depth of the target:

• Near-Surface: Point-blank range
• Very Shallow: Short range
• Shallow: Medium range
• Moderate: Long range
• Deep: Extreme range
• Very Deep: Beyond maximum range (depth charges can't attack here)
• Extreme: Beyond maximum range (depth charges can't attack here)

Depth charges can be used to make salvo attacks, but the effects are different: when depth charges are used to make a salvo attack, each depth charge is set to explode at a different depth (near surface, very shallow, shallow, moderate, and deep), so that one of them will detonate at the correct depth (unless the target is Very Deep or deeper, where depth charges can't reach). No extra damage is done and the area is not increased because the other depth charges all explode at the wrong depth.

Depth Charges (mortar):
These are weapons such as hedgehogs or squids, which appeared around the end of WWII. Just like basic depth charges (which these largely supplanted at time), they have since been completely supplanted by modern homing torpedoes. A large number of smaller depth charges are launched simultaneously, aimed to spread out over a wide area and set to detonate at various depths. They do 4d8 blast damage with area 20 at every depth level from near-surface to deep, and have base range of 100 squares.

Depth Charges (rocket):
These come in two varieties:

• Long-range rockets that carry nuclear depth bombs. They don't need to be super accurate, for obvious reasons. I'm not going to provide rules for these, for reasons I've already explained.
• Weapons that work just like the mortar depth charges I described above, except that they use small rockets to launch the explosives instead of mortars. These work the same as mortar depth charges excpet that they use a different specialization of the gunnery skill (Rockets & Missiles instead of Mortars & Artillery), the base range is 200 squares instead of 100, and they do 4d6 damage instead of 4d8.

Mines:
Mines come in many varieties: free-floating mines on the surface or at a particular depth; moored mines at the surface or at a particular depth (like the mines on chains you see in movies); mines that rest on the bottom and explode or release homing torpedoes when a proximity sensor is triggered; etc. They also come in many sizes, and the fuses can be contact (the spikes on the balls you see in movies), magnetic, acoustic, etc. Given the wide variety of mines and the way they are employed, I think it is best to treat them as traps rather than as weapons.

New Vehicles:
Note: Some of these statistics I feel really confident about, others not so much. Here's a general breakdown of how much stock you should put in my numbers:

• Crew: An amalgam of real-world examples, fudged to fit the standard or expanded progression.
• Pass: An amalgam of real-world examples, fudged to fit the standard or expanded progression. For submarines, passengers are typically special operations forces.
• Cargo: For submarines, this primarily represents foodstuffs and other supplies needed for the crew and passengers. Based on 5 lbs/person/day for the entire complement (crew and passengers) for 60 days (diesel-electric attack), 90 days (nuclear attack), or 120 days (guided-missile), or 180 days (ballistic missile), plus 50% extra for slop, then rounded to a number of tons on the expanded progression. For the destroyer, I used the same method for 60 days, but with 2x slop instead of 1.5x. For the diver sub, I pulled it out of my rear. For the helo, I made a (very well educated) guess, based on the assumption that the only "cargo" would be things that the crew and passengers would bring along for a flight (survival gear, boxed lunches, passengers' personal affects, etc.)
• CTRL Mod: I made up numbers that looked good in comparison to other units.
• Speed (base/max): An amalgam of real-world examples, fudged to make nice round numbers.
• Defenses (Prm/Frt/Ref): I made up numbers that looked good in comparison to other units.
• Hard/DR: I made up numbers that looked good in comparison to other units.
• HP: I made up numbers that looked good in comparison to other units.
• Size: Spot-on for most of the units. Nuclear attack submarines are right on the line between C and 1XC, so I decided to make them C to emphasize the size difference between missile subs and attack subs. Making them 1XC would have instead emphasized the size difference between nuclear attack subs and diesel-electric attack subs, which I didn't think was as important.
• Abilities (Str/Dex/Int): I made up numbers that looked good in comparison to other units.
• Weapons or Special Equipment: An amalgam of real-world examples, fudged to make nice round numbers.
• Adj Level: I made up numbers that looked good in comparison to other units.
• Purch DC: Where I could find numbers online, I used those (cuz everyting on teh internets is true!). Otherwise, I made up numbers that seemed reasonable.

Attack Submarine, Nuclear Powered:

• Crew: 75
• Pass: 10
• Cargo: 30 tons
• CTRL Mod: -10/+16
• Speed (base/max): 4/70
• Defenses (Prm/Frt/Ref): 6/25/2
• Hard/DR: 5/10
• HP: 100
• Size: C
• Abilities (Str/Dex/Int): 15/18/14
• Weapons or Special Equipment: 8x colossal torpedo tubes (F) with 20 colossal torpedoes and 10 colossal missiles (extended range, standard speed).
• Adj Level: 12
• Purch DC: 54(M)

Attack Submarine, Diesel-Electric:

• Crew: 50
• Pass: 5
• Cargo: 10 tons
• CTRL Mod: -9/+14
• Speed (base/max): 3/50
• Defenses (Prm/Frt/Ref): 4/23/2
• Hard/DR: 5/10
• HP: 80
• Size: C
• Abilities (Str/Dex/Int): 12/20/12
• Weapons or Special Equipment: 8x colossal torpedo tubes (F) with 20 colossal torpedoes. Mast launcher with 4x medium missiles (extended range, high speed) (T).
• Adj Level: 11
• Purch DC: 50(M)

Guided-Missile Submarine, Nuclear Powered:

• Crew: 100
• Pass: 50
• Cargo: 50 tons
• CTRL Mod: -11/+18
• Speed (base/max): 4/60
• Defenses (Prm/Frt/Ref): 4/28/0
• Hard/DR: 5/15
• HP: 120
• Size: 1XC
• Abilities (Str/Dex/Int): 18/16/16
• Weapons or Special Equipment: 6x colossal torpedo tubes (F) with 20 colossal torpedoes. 50x colossal missiles (all are standard speed, half are standard range and the other half are extended range) in vertical launch tubes (T). 2 dive locks. Docking clamps for 2 diver subs.
• Adj Level: 12
• Purch DC: 55(M)

Diver Sub:

• Crew: 2
• Pass: 6
• Cargo: 1,000 pounds
• CTRL Mod: -8/+10
• Speed (base/max): 2/20
• Defenses (Prm/Frt/Ref): 5/23/7
• Hard/DR: 5/2
• HP: 30
• Size: H
• Abilities (Str/Dex/Int): 10/12/-
• Weapons or Special Equipment: Crew and passenger compartments are open to the water, and so personnel must use underwater breathing gear. This vehicle provides supplemental breathing gas sufficient to supply the crew and all passengers for up to six hours.
• Adj Level: 4
• Purch DC: 41 (M)

Ballistic-Missile Submarine, Nuclear Powered:

• Crew: 140
• Pass: 20
• Cargo: 100 tons
• CTRL Mod: -12/+17
• Speed (base/max): 4/50
• Defenses (Prm/Frt/Ref): 2/30/-2
• Hard/DR: 5/15
• HP: 150
• Size: 1XC
• Abilities (Str/Dex/Int): 16/14/16
• Weapons or Special Equipment: 4x colossal torpedo tubes (F) with 10 colossal torpedoes. 20x 6XC missiles (high speed, extended range) in vertical launch tubes (T).
• Adj Level: 12
• Purch DC: 56(M)

Guided-Missile Destroyer:

• Crew: 300
• Pass: 30
• Cargo: 100 tons
• CTRL Mod: -12/+18
• Speed (base/max): 4/70
• Defenses (Prm/Frt/Ref): 4/36/-2
• Hard/DR: 5/15
• HP: 200
• Size: 1XC
• Abilities (Str/Dex/Int): 17/18/18
• Weapons or Special Equipment: 30x 1XC missiles (all high speed, half standard range, half extended range) in vertical launch tubes (T). 70x Colossal missiles (all standard speed, 40 extended range, 20 standard range, 10 torpedo missile) in vertical launch tubes (T). 8x Gargantuan torpedo tubes (4 PL, 4 PR) with 20 Gargantuan torpedoes. 1x 5-inch naval gun (PF) with 200 rounds of ammo. 2x 20mm Gatlings (1 PF, 1 PA) with 5,000 rounds each. Helicopter pad and hangars for 2 helos.
• Adj Level: 12
• Purch DC: 52 (M)

Naval Helicoper:

• Crew: 3
• Pass: 3
• Cargo: 500 pounds
• CTRL Mod: -5/+6
• Speed (base/max): 20/300
• Defenses (Prm/Frt/Ref): 7/18/8
• Hard/DR: 5/5
• HP: 40
• Size: G
• Abilities (Str/Dex/Int): 12/12/14
• Weapons or Special Equipment: 4x Hardpoints. 1x 50-cal machine gun in door (PL OR PR) with 1,000 rounds of ammo. Dipping sonar OR 10 sonobuoys.
• Adj Level: 9
• Purch DC: 40 (M)

[lucasjung]

Back in the original Vehicle Combat Thread, I proposed some dogfight rules (well, I proposed a lot of stuff, actually, some of it quite heatedly, but right now I'm talking about dogfights). In that original thread, I championed a more detailed system of rules for vehicle combat, while others preferred a much more abstract system. In the end, Gary took elements from everyone's ideas and came up with rules that are somewhere in-between. I still want to see dogfight rules included as part of the vehicle combat rules, so I've come up with some new proposed rules which are more abstract than what I proposed before, in keeping with the rules Gary put in e20 Lite 0.5.

In the process of coming up with these proposed rules, I realized something: the Hard Turn Maneuver should have some sort of speed reduction built in. You simply can't translate that much momentum from one direction to another without losing some of it. This is very true for aircraft (high-g turns cause dramatic spikes in drag), but I imagine it's also reasonably true for cars as well. I propose the following addition to the rules for the Hard Turn maneuver:

Your speed is reduced by the number of squares you were short of your turn rate, regardless of whether the check succeeds or fails.

Example: Your current turn rate is 10, but you only move 3 squares before using the Hard Turn maneuver. Your speed is reduced by 7 squares.

Before I get to my rules, I'm going to discuss some background, starting with a repeat of parts of my background post from the old vehcicle combat thread. Because the e20 Lite 0.5 vehicle stats don't break out turn rate and turn radius explicitly, I can't have explicit rules for one circle fights vs. two circle fights, so that whole concept will become an abstract part of Control checks. With that in mind, I've deleted those parts of my original background post. Modifications are colored red, while deletions are noted by red dots (...).

As I've mentioned, I'm working on a new "dogfight" system, which will be similar to the SWSE dogfight system in that it will be analagous to a grapple, abstracted as two (or more) vehicles sharing a (mostly) static space on the grid.

As background, I'm going to use this post to talk about real dogfights. As I've said many times, an abstraction must preserve the feel of the real thing, even as it simplifies. The purpose of this post is to help everyone understand the feel of a real dogfight. Of course, there also needs to be some compromise between real dogfights and cinematic dogfights, because most people's expectations for dogfights will be based on the cinematic kinds (and honestly, in a lot of ways, cinematic dogfights are more exciting).

The most important thing you need to understand about dogfights, which overshadows everything else that will be said later:
Dogfights are for suckers.

Ever since the first aerial combat in the early 20th century, military pilots who managed to survive their first few combat encounters all quickly learned that getting into a dogfight is a Very Bad Thing. Instead, they learned all sorts of ways to kill their enemies without actually getting into a dogfight. Why? Because your chances of surviving a dogfight were generally very low. Even if you were really, really good, engaging in a dogfight was extremely risky. Why? Partly because uncertainty, chance, and unequal starting conditions can conspire to let a lesser pilot kill a better pilot in a dogfight. Additionally, you might shoot one plane down, but then get shot down by his wingman. But the biggest reason is...

Because, as pilots often say, Speed is Life. Actually, it would be more accurate to say that energy is life, with speed and altitude being interchangeable forms thereof. When you turn an airplane, especially when you turn it tightly, you increase the drag on your airplane and bleed off speed. In a dogfight, where you are turning as tightly as possible, this happens very quickly. Dogfights also don't happen at a level altitude, either: they tend to spiral downard as the pilots trade altitude for speed so they can keep turning. Even if you win a dogfight, when it's over you will find yourself low and slow, which makes you easy pickings for some other pilot who was smart enough not to engage in a dogfight to swoop down and strafe you. This was actually pretty common in the latter part of WWII in Europe: the veteran pilots on both sides all knew better than to dogfight, but the rookies didn't. The veterans would circle high at a safe distance from each other, waiting for an opportunity; the rookies would go out into the middle and mix things up. Any time someone would pop out of the dogfight, a veteran from the other side would swoop in for a quick strafing run before zipping back up to his perch. That's the smart way to kill an enemy: start the fight higher and faster (i.e. with more energy) than him, and use that to make quick attack runs on him, then break off before it turns into a dogfight. If you can, start from behind him so that you also have the element of surprise.

However, it's good to know how to win a dogfight, because sometimes you will be drawn into one whether you like it or not. The most important thing to understand is ... excess power. ... Excess power is rather complicated, but we'll just say that it's a measure of how fast you can accelerate and/or climb.

...

What do you do if the other plane has both smaller turn radius and higher turn rate than your plane? It doesn't matter whether the fight is one circle or two circle, either way you are at a disadvantage. The answer is obvious: don't get into a turning dogfight with that plane! American pilots learned this lesson the hard way in the Pacific theatre of WWII, and again in Vietnam. The solution is to have higher excess energy than the other plane (if you don't even have that, you'll have to resort to creative team tactics and/or superior numbers). In both of those wars, the American planes could not turn as fast or as tight as their enemies, but they had really big engines. They soon learned that turning with the enemy was a Really Bad Idea; instead, they took their dogfights into the third dimension. Their big engines allowed them to climb faster than their enemies, so rather than just turning left or right, they would also turn up. They could climb at a steeper angle, so they would stay above their enemies' line of fire. Once they had built sufficient vertical separation, they would pitch back over and make a diving attack, a maneuver called the "yo-yo." Another tactic involved some teamwork: one pair of planes would fly to the merge, with another pair hanging back a little. The first pair would not turn at the merge, but would rather blast straight through at full throttle, while the enemy would turn around to get behind them. However, this turn would leave the enemy significantly slower, so they would lag behind. Then the second pair of American fighters would come up and make an easy strafing run against the now-slow enemy planes from behind. All of the American planes would continue out to a safe distance before turning around to come back in and do it all again.

In a dogfight, you can be in one of three general conditions: neutral, offensive, or defensive. "Neutral" means neither you nor your opponent is in a position to fire: you are "across the circle" from each other (of course, with some modern short-range missiles, "neutral" means that both planes are in a position to fire). "Offensive" means you are in a position to fire, but your opponent is not. "Defensive" means your opponent is in a position to fire, but you are not. If you're neutral, both you and your opponent are trying to gain the advantage and become offensive. If you are defensive, then you are either trying to escape the dogfight (most likely in a real dogfight) or return the fight to neutral (most likely in a cinematic dogfight).

...

So, how is all of this relevant? I want an abstract dogfight system which:

• Includes the concepts of "offensive," "neutral," and "defensive," with ways for pilots to try to shift the balance of power. This is very analagous to "pins" in grapples. Unlike grapples, there should be a way to enter a dogfight already "offensive" (e.g. by "getting the jump on the other guy")
• ...
• Includes a way for an pilot to escape from a dogfight when he knows he is losing.
• Includes a mechanic for the effects of g-forces, so that pilots experience adverse physical effects from pushing their aircraft too hard.
• Gives significant advantages for numerical superiority in a dogfight. (teamwork matters, a lot!)
• Leaves the victor slow and vulnerable at the conclusion of a dogfight.

Some of this is already in the SWSE dogfight rules, but a lot of it isn't.

My new proposed dogfight rules will treat a dogfight as an energy management problem: you start the dogfight with a certain amount of kinetic energy (speed) and potential energy (altitude). You burn these up trying to get behind your opponent(s). Any dogfight that drags on long enough will end when one plane runs out of energy, leaving it essentially helpless at the hands of the other plane. However, some dogfights will end sooner if one plane is able to gain the advantage even before the other plane runs out of energy. During the course of a dogfight, you can choose to spend your energy more quickly in order to try for the quick kill, but if you fail to get that kill you are dooming yourself to lose by default when you run out of energy first.

Going Vertical:
In my original background post, I mention how American pilots in WWII and Vietnam would use their bigger engines to take dogfights into the third dimension, and mentioned a specific maneuver of this type (the "yo-yo"). In general, this type of tactic (the "yo-yo" as well as other maneuvers) is referred to as "going vertical." This will be a big part of my proposed dogfight rules, but there are some important details to understand as background.

First, you have to wait for the right time to go vertical. When you go vertical, you are trading kinetic energy (speed) to gain potential energy (altitude). That means you slow down, a lot. Being slow makes you an easy target if your opponent can get his nose pointed high enough to aim at you. So, if you go vertical too early in the fight, when your opponent still has lots of speed, he can just follow you up and now he's on your tail with an easy shot. Instead, you have to wait until he no longer has enough speed remaining to point his nose up, and then you can go vertical safely.

When it comes to "going vertical," the 500-lb Gorilla is Thrust in Excess of Weight. I introduced this concept in an earlier post in this thread, but I'll explain it again here: an aircraft with thrust in excess of weight can literally point straight up and continue accelerating because the upward force produced by the engines is greater than the downward force produced by gravity. A plane without this advantage can only "go vertical" by trading airspeed to gain altitude, meaning that it can only climb a certain distance before it must level off. A plane with thrust in excess of weight doesn't have to trade when it "goes vertical:" it gets to add altitude without giving up speed. In reality, there are practical limits on this:

• Typical real-world aircraft with thrust in excess of weight only achieve that much thrust in afterburner, which sucks down gas at an incredible rate.
• An aircraft's weight isn't constant, it's a function of how much fuel it's currently carrying and (for combat aircraft) how much ordnance. Typical real-word aircraft with thrust in excess of weight don't actually have more thrust than weight until they have expended some ordnance and burned off a lot of fuel.
• As altitude gets too high, thrust from a jet engine decreases rapidly, so there is a partical limit on how high an aircraft can climb in this manner.

In summary: a real-world aircraft with thrust in excess of weight can't actually fly straight up until relatively late in the dogfight, can't fly straight up for very long, and can't exceed its maximum altitude even when flying straight up. The first two effects are caused by fuel limitations, but (as I said in my post outlining optional fuel rules), fuel management adds a generally undesireable level of complexity to vehicle combat. Instead, I had to come up with other, artificial limitations on the use of thrust in excess of weight.

Thrust Vectoring
In the real world, this is an even bigger deal in dogfights than thrust in excess of weight (and as far as I know, all of the combat aircraft built with thrust vectoring also have thrust in excess of weight, so it's a double-whammy). I also proposed this as a vehicle trait in an earlier post in this thread. As described, my proposed trait gives a significant advantage in dogfights (the ability to continue flying below the normal min speed for your aircraft). The other advantages of thrust vectoring (such as tighter turns) could be represented by higher bonuses to control checks.

That's enough background. Time for (proposed) rules!

Map Scale
Aerial combat with missiles will typically take place using the aerospace map scale. On that scale, all combat aircraft are little. A Gargantuan fighter jet will also be little at tactical scale (which I proposed renaming "operational") but will take up exactly one square at local scale (which I proposed renaming "tactical"). Modern fighters engaging in missile combat typically fly at high subsonic or low supersonic speeds (in other words, Mach 1 +/- a little bit), which works out to about 1 square per round at aerospace scale. Once they get involved in a dogfight, they slow down rapidly as they maneuver, typically trying to maintain a speed in the ballpark of 500 squares/round, which happens to be 1 square/round at tactical scale or 10 squares/round at local scale (where the jets are no longer little). 10 squares/round might seem like a lot on a map that is only 24x36 or so, but when you consider the fact that the planes will be turning hard the whole time trying to get behind each other, it's really not that much. So one way to handle a dogfight would simply be to "zoom in:" leave a marker on the main map (the one at aerospace scale) to show where the dogfight is taking place, then move the fighters involved to a "side map" at tactical or local scale. You could then just use the normal vehicle combat rules to play out the dogfight. However, this requires significantly more table space and can take a lot of time. If many separate dogfights are happening simultaneously as part of a larger aerial battle, resolving dogfights by "zooming in" would be completely impractical. For situations where "zooming in" is inappropriate, I'm proposing the following abstract dogfight rules for use at map scales where the vehicles are little.

Dogfight Positions:
In addition to speed category and altitude level, an aircraft in a dogfight has a "position" relative to its opponent(s):

• Victorious: An aircraft in this position is perfectly lined up behind the opposing aircraft to make a kill shot. The opposing aircraft is in the "defeated" position and is considered helpless to the victorious aircraft.
• Offensive: An aircraft in this position is able to attack the opposing aircraft, but not necessarily lined up for a perfect shot. The opposing aircraft is in the "defensive" position and is considered disadvantaged to the offensive aircraft.
• Neutral: Neither aircraft is in a position to attack the other; they are "across the circle" from each other. The opposing aircraft is also in the "neutral" position.
• Defensive: An aircraft in this position is subject to attack by the opposing aircraft and is considered disadvantaged to the opposing aircraft. The opposing aircraft is in the "offensive" position.
• Defeated: An aircraft in this position is no longer able to effectively defend itself from the opposing aircraft and is considered helpless. The opposing aircraft is in the "victorious" position.

Initiating a Dogfight: EDIT: Just remembered that there are no full-round actions in e20. Changed this to comply.
Any time an aircraft ends its movement in the same square as one or more opposed aircraft at the same altitude level or an adjacent altitude level, a dogfight begins. If the aircraft that moved into the square has not yet used its standard action for that turn, it may make a standard action immediately after joining the dogfight.

The dogfight always stays stationary in the square where it started.

Aircraft in a dogfight no longer track exact speed and altitude, instead just tracking speed category and altitude level. When an aircraft enters a dogfight it has the speed category of its last declared speed and the altitude level of its last altitude.

At the beginning of a dogfight, all aircraft are in the neutral position unless the aircraft that initiated the dogfight (by ending its turn in the same square as another aircraft) meets all of the following conditions:

• Has higher initiative than its opponent.
• Is at the same altitude or higher than its opponent.
• Enters its opponent's square from behind its opponent.

If the initiating aircraft meets all of these conditions, it starts the dogfight in the offensive position and its opponent starts in the defensive position.

Losing Energy:
Aircraft in a dogfight are turning hard, constantly. This causes them to lose speed rapidly. At the end of each round, when a pilot would normally declare his speed for the next round, his speed is instead automatically decreased by one speed category. Pilots who are already at minimum speed should plan ahead and use the Descend dogfight maneuver to gain enough speed to avoid losing control at the end of the round.

If an aircraft is at very low altitude and minimum airspeed, any further reduction in airspeed would result in loss of control (and a subsequent crash), while any further reduction in altitude would result in a crash. In this situation, the pilot's only choice is to fly straight and level, leaving him extremely vulnerable to his opponent. In game terms, the aircraft is shifted automatically and immediately to the defeated position, but gains one speed category instead of losing one.

G-forces:
All of those hard turns take a toll on pilots, physically. At the end of each turn, a pilot in a dogfight must make a Fortitude Save or become Fatigued.

Range Penalties:
If you are at the same altitude level as your target or one level higher, the attack is considered to be at point blank range. For every altitude level higher than your target beyond the first, or for every altitude level lower than your target, the range increases by one increment.

Loss of Control:
If an aircraft in a dogfight loses control, it does not follow the normal rules for uncontrolled aircraft. Instead, it remains in the dogfight. The opposing aircraft immediately gets to make an attack of opportunity against the aircraft which loses control. After that, the uncontrolled aircraft automatically and immediately shifts to the defeated dogfight position. The uncontrolled aircraft loses one altitude level at the end of each turn until it either regains control or crashes.

An uncontrolled aircraft can only take one action each turn: attempt to regain control. This is a DC 15 Control (Dex) check. On a successful check, the aircraft regains control and has Low airspeed, but remains in the defeated dogfight position. An aircraft can take a single move action on the turn that it regains control, after regaining control.

Dogfight Actions: EDIT: Just remembered that there are no full-round actions in e20. Significant changes to this section in order to comply.
Aircraft in a dogfight are extremely limited in their choice of available actions: they can only take the actions listed below, plus attacks of opportunity. Some actions are only available to aircraft in particular dogfight positions. The standard actions available to aircraft in dogfights are:

• Change Position: With this maneuver, you try to get into a more advantageous position relative to your opponent. Make an opposed Control (Dex) check against your opponent. On a successful check, your position moves one step up on the position scale. On a success by 5 or more, you move two steps up on the position scale. On a failed check, your position does not change. On a failed check by 5 or more, you move one step down on the position scale. However your position changes, your opponent's position changes correspondingly. A tie is considered a failed check.
  Allowed Positions: You may take this action from any position.
  Altitude Advantage: If you are at a higher altitude level than your opponent when you make this check, you get a +5 bonus.
  Pull Harder: Before rolling, you may choose to reduce your speed by one category in order to gain a +5 bonus to this check. This increases G-forces, so you take a -5 penalty on your Fortitude save to avoid fatigue at the end of your turn. Your opponent may also choose to pull harder.
• Attack: You make a basic attack or talent-based attack against your opponent.
  Allowed Positions: You may take this action from the offensive or victorious position. If made from the victorious position, you may chose to make a coup de grace attack because your opponent is helpless.
• Escape: With this maneuver, you attempt to disengage from the dogfight. Make an opposed Control (Dex) check. On a successful check (a tie is considered a success), you escape and the dogfight ends; roll a d8 to determine your new direction of travel (see table). Determine your opponent's direction of travel according to the magnitude of success (see table). Your new airspeed is equal to the minimum speed for your current speed category and your new altitude is equal to the minimum altitude for your current altitude (or 10 ft, if you are at Very Low altitude). Your opponent's airspeed and altitude are determined in the same manner. Both you and your opponent each move forward at your new speed and direction, after which your turn ends.
  
  Escapee Direction Table (on d8 roll):
  1: North
  2: Northeast
  3: East
  4: Southeast
  5: South
  6: Southwest
  7: West
  8: Northwest
  
  Opponent Direction Table:
  *Escapee rolled 0 to 4 higher than opponent: opponent's new direction is 45 degrees off from escapee's (opponent's choice of which side).
  *Escapee rolled 5 to 9 higher than opponent: opponent's new direction is 90 degrees off from escapee's (opponent's choice of which side).
  *Escapee rolled 10 to 14 higher than opponent: opponent's new direction is 135 degrees off from escapee's (opponent's choice of which side).
  *Escapee rolled 15 or more higher than opponent: opponent's new direction is 180 degrees off from escapee.
  
  Allowed Positions: You may take this action from any position except defeated. If you are in the defensive position, you take a -2 penalty to this check. If you are in the neutral position, you get a +2 bonus to this check. If you are in the offensive position, you get a +5 bonus to this check. If you are in the victorious position, you get a +10 bonus to this check.
  Pull Harder: Before rolling, you may choose to reduce your speed by one category in order to gain a +5 bonus to this check. This increases G-forces, so you take a -5 penalty on your Fortitude save to avoid fatigue at the end of your turn. Your opponent may also choose to pull harder.
• Regain Control: Discussed above.

The move actions available to aircraft in dogfights are:

• Descend: With this maneuver, you trade away altitude to gain airspeed. Your altitude is immediately reduced by one level. Make a DC 20 Control (Str) check. On a successful check, your speed increases by two categories. On a failed check, your speed only increases by one category.
  Allowed Positions: You may take this action from any position.
• Climb: With this maneuver, you trade away airspeed to gain altitude. Your airspeed is immediately reduced by one speed category (unless you have the thrust in excess of weight trait, in which case your speed is unaffected). Make a DC 15 Control (Str) check. On a successful check, your altitude increases by one level. On a success by 5 or more, your altitude increases by two levels. On a failed check, your altitude does not change. On a failed check by 5 or more, your aircraft becomes uncontrolled (unless you have the thrust vectoring trait, in which case you do not lose control).
  Allowed Positions: You may take this action from the neutral, offensive, or victorious position. If you take it from the neutral position with your opponent at the same altitude level or higher, your opponent gets to make an attack of opportunity against you as a free action before you make your Control check. If you take it from the offensive or victorious position, you move one step down on the position scale and your opponent moves up correspondingly.

The only other actions available to aircraft in dogfights are attacks of opportunity. Conditions when an aircraft gets to make an attack of opportunity are discussed above.

Firing Into a Dogfight:
Aircraft in a dogfight are considered disadvantaged to all aircraft outside of the dogfight. However, aircraft in a dogfight are also considered to have mobile cover from the other aircraft involved in the dogfight. If an attack against an aircraft in a dogfight misses by 2 or less (the cover bonus from being in a dogfight), it hits an aircraft opposed to the intended target. If there are more than one opposed aircraft, select one randomly. Also, attempts to gain target lock on aircraft in a dogfight have +5 to DC and attempts that fail by 5 or less instead lock on to an aircraft opposed to the intended target.

Joining a Dogfight:
When multiple allied aircraft are in the same dogfight together, they fight as a unit called a flight. Each side is working as a team to get one plane from the flight into a position to fire against one plane from the opposing flight, so the positions take on slightly different meanings:

• Victorious: One aircraft from this flight is perfectly lined up behind one aircraft from the opposing flight to make a kill shot. The opposing flight is in the "defeated" position and is considered helpless to the victorious flight.
• Offensive: One aircraft from this flight is able to attack one aircraft from the opposing flight, but is not necessarily lined up for a perfect shot. The opposing flight is in the "defensive" position and is considered disadvantaged to the offensive flight.
• Neutral: Neither flight is in a position to attack the other; they are "across the circle" from each other. The opposing flight is also in the "neutral" position.
• Defensive: One aircraft from this flight is subject to attack by one aircraft from the opposing flight and is considered disadvantaged to the opposing aircraft. The opposing flight is in the "offensive" position.
• Defeated: One aircraft from this flight is no longer able to effectively defend itself from one aircraft from the opposing flight and is considered helpless. The opposing flight is in the "victorious" position.

The aircraft in a flight all act as a team. The entire flight acts at the same time, using the highest initiative in the flight (the other aircraft don't change their initiative, they just "borrow" initiative for the duration of the dogfight). All aircraft in the flight share the same speed category and altitude level (if there is conflict, use the lowest speed and lowest altitude). All of the aircraft in the flight take the same action each turn. If there is more than one PC in the flight, the PCs alternate turns deciding which action to take. Every check made by the flight is made by each pilot independently, then the flight uses the highest result.

When a flight attacks, the PC who made the decision to attack gets to choose which specific opposing plane to target. If a flight attacks from the victorious position and destroys an opposing aircraft, the attacking flight automatically and immediately drops to the offensive position: they still have the upper hand in general, but the one plane they were in a really good position against is now gone and they will have to work to get another enemy plane into such a compromised position.

Additional aircraft may join a dogfight by ending their movement in the same square as the dogfight, at the same altitude as their allies in the dogfight, or one altitude level higher. The joining aircraft's speed and altitude are set to match the speed and altitude of its allies, so that all of the aircraft in each flight have the same altitude and airspeed. If the joining aircraft has higher initiative than any of its allies, and if it has not yet used its standard action for the turn, its flight gets to take their action for the round on the new aircraft's initiative. Otherwise, they don't shift to the new aircraft's initiative until the next round.

[lucasjung]

The other day I was thinking about ejection seats, which led me to think about parachutes. A parachute falls at about 23 ft/sec, depending on a few variables such as the mass of the person hanging under it (at least, that's about how fast ejection seat parachutes fall--other types of parachutes may be designed for different terminal velocities). Just to put that into perspective, that means that when you hit the ground under one of these things, you're falling about as fast as you would be if you had jumped from a second-story window. That's why you see jumpers do a sort of flare maneuver when they land. That maneuver takes training and experience to do right, so people who will have to jump without all that training and experience are trained instead to perform a Parachute Landing Fall (PLF), a much cruder method whereby you hit the ground at the full speed of 23 ft/sec and break your fall by bending your legs, falling on your butt, and rolling onto your side/back. It still leaves you bruised, but if done correctly will prevent broken bones.

23 ft/sec is about 28 squares/round. Rounding that to the nearest step on the standard progression gets us 20 squares/round, which converts back to 17 ft/sec--still in the ballpark of jumping from a second-story window. So here are some super-simple parachute rules:

A parachute falls at a rate of 20 squares/round. A parachute takes one full round to open, so on the round when it is opened the character using it falls as if he had no parachute. On the second and subsequent rounds, he falls at a rate of 20 squares/round. We could also add some optional rules for parachute malfunctions. My initial tendancy would be to come up with separate effects for each of the primary types of malfunctions, but it would probably be better to just have "Major Malfunction" (it's not working at all) and "Minor Malfunction" (you fall at 50 squares/round instead of 20).

If you do nothing when landing a parachute, the normal rules for falling damage apply, as if you had fallen 20 feet. You can make a Control (Dex) check to avoid this: DC 15 to take falling damage as if you had fallen 10 feet instead of 20, succeed by five or more for no falling damage.