Tuesday, October 16, 2018

Action Vehicular Combat - Musings

One of the reasons I wanted to step away from GURPS Spaceships is that it seems less compatible with the GURPS Action rules than I would like, and I didn’t want one rule-set for outspace and one ruleset for the ground. In principle, a repulsor-car chase and a dogfight should be essentially the same.

I’ve dug through the chase rules, and the Dogfighting rules from Pyramid and, of course, I’m already familiar with the Spaceship combat rules. My intent here was to get a feel for how things worked, and what I’d want to change if I wanted to use the rules for Psi-Wars. My core discovery is that the Chase rules are for chases, and what I really want is a vehicular combat system. The chase rules comment several times on what happens when you “Catch up” to your target: combat happens. Fortunately, the chase rules support combat, allowing the game to flow in and out of combat and chases:

Chases and combat aren’t exclusive! The chase rules support combat during a chase, and the GM is free to end a chase if both sides decide to stop running and start shooting. Similarly, if somebody bolts from a fight, the GM can switch over to the chase rules -GURPS Action 2 page 31

So if we want a more comprehensive example of what a Psi-Wars Dogfight or Tank battle looks like, what we ultimately need to do is work out how vehicular combat should work in GURPS Action, as the GURPS Action doesn’t really consider this, focusing more on cars and motorcycles than tanks and fighter jets.

Incidentally, a quick aside: one thing I’ve struggled with in GURPS Action is how to handle movement. If you’re at rifle range and you want to move to melee range, how do you do it? The answer has been staring me in the face the whole time: you trigger back into the chase rules. Duh. This actually means moving into melee is actually pretty easy.

Core Assumptions of GURPS Action

When it comes to chase scenes, the game assumes that turns take up to a minute (it is intentionally vague), and that we have various range-bands. “Dogfighting Action!” assumes a minimum distance, typically Extreme. GURPS Action doesn’t really discuss “facing,” but Dogfighting action states that the “winner” faces the target and the “loser” does not. Another fair assumption is that if one is fleeing, their back is showing to the pursuer, whose front faces the target. The chase rules allow attacks, but the assumption is that while one might be firing the whole time, only a few shots “count” and those shots are the single attack made during the “Turn.” You’re also only allowed to attack during an Attack or a Move and Attack (or, as passengers, during Rams, Forces and Disembark/Embark).

Understanding Ranged Attacks

GURPS Action 2 requires those in a vehicle to attack at a -2 penalty or the bulk or their weapon whichever is worse (a “move and attack”) and disallows aim. GURPS Spaceships explicitly allows aiming (and assumes at least 3 seconds worth of aiming) and grants fixed mount weapons a +2 to hit, while turret weapons have a +0.

We’re mostly concerned with turrets and fixed mounts, as most vehicles will use one or both of these. According to B467, “Turrets” have no special rules, but Fixed Mounts must have facing, and the operator rolls against the lower of his Gunner or Control skill to hit. The other difference between the two is noted on page B548 under “Attacking from a Moving Vehicle.” For aerial vehicles, this is -1 for hand-held weapons and +0 for all other weapons; for water vehicles, a stabilized turret is at -0 while a fixed mount is a -1, and for an off-road ground vehicle, a stabilized turret is -1 and a fixed mount is -2.

This clearly disagrees with GURPS Spaceship’s +2 for fixed mounts, limiting the skill roll of the fixed mount gunner and generally applying a -1 above what a turret firer suffers. Where is the bonus for GURPS Spaceships coming from? Well, their description of Fixed Mounts on page 26 of Spaceships gives us a clue:

However, superior focusing or stabilization systems give fixed mounts better range and fire control (a +2 to hit).

The first thing to notice is that it notes that superior focusing or stabilization systems give the fixed mount its superior accuracy, not the fixed mount itself. This might be a reference to how GURPS Vehicles works. For a 1-ton fixed mount, you need 40 cubic feet (and the mass associated with the structure necessary to support those 40 cubic feet). For 1-ton gun in a full-rotation turret, you need 48 cubic feet. GURPS Spaceships might hand-wave away both as “about 50 cubic feet,” and grand additional accuracy-bla-bla to take up the remaining 8-10 cubic feet. Note, also, the “however” in the quote above. This suggests that the rule balances out the fact that a fixed mount can fire in only one direction, because why equip fixed mounts at all if turrets are just as good? In Vehicles, this is because of that lost volume and mass, but Spaceships doesn’t have that granularity, and so it needs to offset the downsides to a fixed mount, and this is how it does that.

So it seems that “Dogfighting Action!” is correct: fixed mount weapons don’t get a bonus. If anything, they should get a penalty! I like the idea of the piloting skill acting as a limiting value, but I worry that would over-rate the already exceptionally useful Piloting skill! It’s hard to differentiate one pilot from another if the game requires all characters to have the same skill! It’s also an extra layer of complexity. Thus it seems clear that Dogfighting Action’s handling of turrets vs fixed mounts is correct (and likewise, its handling of hardpoints: Let’s just ignore the -1 acc unless we’re mounting guns!)

But what about the -2 move and attack penalty? According to B470

Do not apply [the move and attack] penalty to mounted weapon attacks, ramming attempts, or vehicular melee attacks.

This is why I argue that GURPS Action assumes that all attacks during a chase are with hand-held guns, because the rules cover hand-held guns! This means that Mr. Pulver is correct again in “Dogfighting Action!”, your vehicle does not suffer a move and attack penalty.

Passengers do suffer a -2 or -4 penalty if the vehicle dodges (not the vehicle operator!). This is not in the GURPS Action chase rules, which instead gives the passengers a flat -1. This may be because of the way the game handles time. If a brigand in a truck opens fire at a cop-car and the cop-car dodges, the cop’s partner doesn’t fire then because she’s being jostled too much, but once the car has settled down, she may take some shots at the brigand. All of this is covered by the “-1 for passengers.”

What about aimed attacks? GURPS Spaceships always allows them, “Dogfighting Action” seems to ignore them, and GURPS Chase rules only allow it when you stop moving. Is there any way to aim? Well, according to Basic: yes, but you’re limited by SR unless you’re using a stabilized weapon. So why doesn’t the Chase rules allow it? Well, under Attacks on page 35:

“Only Attack, Disembark/Embark, Force, Move and Attack, and Ram allow attacks. During other maneuvers, either your target isn’t in sight or your movement is too wild to allow a shot.”

This also explains why we don’t have Mobility Attacks (they represent shortcuts that your opponent cannot take, and that puts your target out of sight) or Stunt Attacks (Your movement is too wild), which answers one question I had, but at the same time, it reveals something I didn’t know:

“Heroes with Gunslinger can shoot during any maneuver but Hide!”

Woah! That’s amazing! So a Gunslinger can shoot at basically any time. He also gets accuracy where others wouldn’t. I personally think this should only apply to gunfire from handheld weapons. For mounted weapons, we need some sort of different advance, like “Ace Pilot” or something.

Ranges, Speed and Collision

One thing I found odd and interesting about “Dogfighting Action!” is that the system limited the fighters to Extreme range. Why is this? Well, as best as I could tell, it has to do with how range and speed modifiers are calculated. If we check “Target’s Speed and Range” on B551, it argues that we should sum the speed and range of the target and use that sum to find the modifier. Thus, a a car that travels at 25 yards per second (-6) and is 10,000 yards away (-22), the penalty is -22 (10,025 yards) not -28. Similarly, if you’re shooting at a super-sonic jet fighter going 500 yards per second (-14) that’s ten yards away (-4), the total penalty is -14 (510), not -18. These values might shift one way or another by a point, depending on how you round it, but it won’t make much of a difference until you bring those two values close together: a 500 yard per second craft at 500 yards away has a total of “1000 yards” and thus while each individual trait is -14, the final value is -16. This additional -2 is the worst such a penalty will be, and this is about where Pulver recommends you limit the range of the vehicle: given that these vehicles move faster than 500 yards per second at top speed, being closer to one another than 500 yards means they can slam into one another in less than a second: our speed begins to matter more than our range!

Taken together, this suggests that your ranged attack penalty should always be the worse of your range penalty or your target’s speed bonus as a penalty.

GURPS Spaceship does introduce a “Collision Range” which is an interesting concept. “Dogfighting Action!” mumbles something about forcing another target by tapping wings or something similar, but how close do you need to be? We can bring the concepts together: when your speed bonus is larger than the absolute value of your range penalty, you are in “collision range” because speed matters more than your range (and you can also cover that distance in less than a second). At this range, you may perform any action that requires you to be “Close,” including forcing, ramming and is the result of a reverse.


Many vehicles care about facing. A tank has more armor in the front than in the back; vehicles with angled force screens determine which direction those screens face, and vehicles with fixed mounts can only fire in a single direction.

GURPS Action makes no distinction about the direction the vehicles chase. This is likely because for vehicles like cars, motorcycles and other typical “chase scene” vehicles, this doesn’t matter. Your action hero might be escaping by driving backwards, so his front faces his pursuers because it’s cool. Sure, that can happen in the Action rules as written, and don’t matter as far as the chase rules are concerned.

They do start to matter for vehicular combat. A character can reach out of a window and fire his gun in any direction, but a car with machine guns attached to the top cannot. A lot of the maneuvering of a dog fight is an attempt to get behind the opponents, so that his weapons cannot fire on you, while yours can fire on him.

So, the question is: how do we determine facing, especially in dynamic situations, like trying to get above another fighter, or to attack the side of a vehicle that is trying to keep you behind it or in front of it. GURPS Spaceships has a few suggestions, as does the “between the lines” of “Dogfighting Action!”

  • If you succeed at a “Chase” roll and reduce range, your front is pointed at the other vehicles.

  • If you succeeded at a “Chase” roll and increase range, your back is pointed at the other vehicles.

That much is obvious. What’s also implied here is that if your intent is to increase range or reduce range, then you have the same facing. That is, if you try to escape, your back is facing the other vehicle whether or not you succeed. GURPS Spaceships treats facing as an aspect of a maneuver choice (The evasive and escape maneuver have your back facing the target).

This creates an interesting situation that contrasts GURPS Spaceships with “Dogfighting Action!”. In the former, both combatants choose their facing. It’s possible for both fighters to face one another for the entire battle; this is less a case of two fighters just staring each other down, but more that they “swoop” past one another at high speeds, and both turn as one to make another “jousting pass.” In “Dogfighting Action” the one who succeeds at the maneuvering roll dictates the facing of both himself and his target: he can shoot but his rival cannot. It should be noted that GURPS Spaceships 4 offers a compromise between these two positions with “Airplane-Style Dogfights” where if your opponent gained Advantage on you, you cannot choose to “close” and thus cannot “face” your target.

This suggests a Spaceships’ like model. You can either attempt to “Close” with your opponent, in which case your “front” faces your target; or you can attempt to “Escape” your opponent, in which case your “Back” faces your target. If you can outmaneuver your opponent, you might gain some “Advantage” which might do a few things, but one of those things might be to let you choose your opponent’s facing. If you have a Stall speed, you cannot “Close” on a target that had advantage on you in the previous turn.

All-Out Move or All-Out Move and Attack

One thing that came up as I worked through the Chase rules is that the Chase Roll Result gives equal weight to speed and handling, but the vehicle rules give extra weight to Handling (which assists in dodging). This makes Handling superior to Speed for chases. Is this okay?

If you have a vehicle with a Speed bonus of +1 (3 yards per second or 6 miles per hour) and a Handling of +5 (say, a extraordinarily agile hoverboard) in a chase with a vehicle that has a speed of +11 (150 yards per second, or 300 miles per hour) and a Handling of -5 (say, a rocket-sled with no steering or meaningful brakes), they would be dead even in chase rolls, which might strike you as absolutely stupid, but that really depends on your circumstances. The rocket-sled can only go straight. If your race is on a flat and open field, then obviously the rocket sled wins, but if we’re in a cluttered city-scape, which is what GURPS Action assumes, then the Rocket Sled’s crazy speed only counts for so much if it needs to turn and can only do so by stopping, having the guy get out, turn it in the new direction, and hop back in and accelerate away, while the hoverboard can only putter along but can turn on a dime, jump, dodge, juke, etc.

How can I fix this? What am I even trying to fix? There seem to be situations, like on a straightaway, where raw speed matters more than your agility or your ability to maneuver. Taking an “All-Out Move” might make your speed matter more in some way. But how do you prevent people from using it in circumstances where it isn’t a straightaway. For example, what prevents someone from going “flat out” in a crazy situation full of obstacles, like on-coming traffic? The answer there, I’m afraid, is “nothing,” and in such situations, your handling matters a great deal, because superior handling and skill allows you to maximize your speed in situations where others wouldn’t be able to maximize speed, and maximizing your speed in dangerous situations where a failed roll could make you “wipe out” is the definition of a stunt.

So what are we left with? We’re left with the fact that in certain situations, speed matters more than handling. An example might be on a long, straight highway, or in the air if a fighter wants to escape. In such situations, where those involved are far enough away from one another that maneuvering doesn’t make a difference, the vehicle with the faster speed dictates what occurs. And that’s a simple enough rule to simply state: If you’re faster than the other guy, there are no obstacles and maneuvers won’t help you, then you just escape. If he’s faster than you, then you just don’t.

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