Vehicle Combat in MTDAA the RPG

In my summer school class, I am reading Unbroken with my students. It's the first time I've had a chance to read it, and I find its descriptions of going on bombing raids and what things are like inside of a bomber fascinating. There are two big takeaways in terms of emulating such combat in a RPG like Army Ants...

1. The vehicle doesn't always protect those inside. My default assumption has been that, if you are inside of a vehicle, you are generally protected from suffering damage until the vehicle itself is disabled - or close to being disabled. That is, clearly, historically inaccurate. 
2. Vehicles don't have 'hit points' like I've traditionally used them; a vehicle could take a little shot that hits a sensitive system or ruptures a fuel line, and your problems suddenly multiply. Or, as is the case in the book, a vehicle can sustain unbelievable damage, several members of the crew can be horribly wounded, and the thing can keep on flying. You land and then the wing falls off.

It seems logical to replace an armor class and hit point system with a series of saving throws (or Feats as I label them). Since MTDAA relies on escalating dice, and allows dice to explode, you could use a pretty simple mechanic that includes a handful of ratings. I think that a vehicle really only needs control, chassis, and durability ratings in terms of combat applications.

Control is a check the pilot makes any time something bad might happen, including getting shot down, evading a missile strike, landing in difficult conditions, or the like. A vehicle has a modifier to checks, which are based on the pilot's abilities and the circumstances.

The chassis would be a lower number, between 2 and 10. This would be the minimum damage an enemy would need to do to possibly disable the vehicle. Let's go with a combat helicopter for our example. It's not exceptionally armored like a tank, but it's got some plating. We'll go with 4 for its chassis. Any damage below this amount is negligible.

The durability is a dice value. A low-durability vehicle (a glider or raft) has D4, while a jeep might be D6, and a tank might be D12. We'll put our combat helicopter at D8.

A vehicle's damage starts at 0, and increases as it suffers damage in combat.  

Combat Helicopter: Control +2; Chassis 4; Durability D8

Let's say that a basic anti-aircraft gun has D6 for damage. Our helicopter moves within range of such a gun, and takes fire. For our purposes, we'll say that, before it can get out of range, the helicopter gets hit three times by this gun (there were five attacks, but three of these were beyond the pilot's Prowess + Pilot + Control checks). 

The first attack deals 3 damage, and since this below the chassis of 4, there's no significant damage. Everyone inside is fine.

The second attack deals 5, and since this is above the chassis of 4, the helicopter suffers 1 damage. This forces a durability check, and as long as you don't roll below 1 (which is impossible), all is well. So, all's well by default. 

However, someone inside might have been injured anyway. We'll say that any time a vehicle sustains damage, there is a chance that those inside are injured in some way. Everyone should attempt a Prowess Feat, DT 6 + the damage suffered that round. In this case, that would be DT 7. We can say that any vehicle damage that affects a passenger would deal a standard D10 damage (easy to remember, and the potential to be pretty signficant); this die can explode. We'll say that everyone makes the Prowess Feat and gets lucky.

However, the third shot is a natural 6, which explodes, followed by another 6, also exploding followed by a 4. This is a total result of 16. This is is more than 10 beyond the Chassis, it's 2 damage, bringing the total damage to 3. Now, there's some concern; the pilot cannot roll a 1 or 2, because then the helicopter is potentially disabled. Let's say that the pilot rolls a 2; the helicopter begins spraying fuel from a ruptured line.

This requires a control check. We'll say that these checks are always based on 6, and then modified from there by the damage. In this case, the DT is going to be 9 because of the 3 damage the helicopter has sustained. The pilot makes the check (his Prowess D8 + Pilot 3 + Control 2, and he rolls 5 for a result of 10), and is okay. He manages to turn off that fuel injector and re-route to another line. 

Additionally everyone inside must attempt a Prowess Feat, CR 6 + the damage sustained that round. In this case, the damage was 2, so the Feat is DT 8. Anyone who fails that Feat suffers D10 damage, and that damage can explode. We'll say that of the crew of three (pilot, gunner, and navigator/engineer), the gunner is hit for 10 damage, which explodes for another 6. This is enough to reduce him to negatives, but he survives. 

If the pilot had failed, the helicopter would have lost fuel, and would crash in 1D6 rounds; the pilot would need to make another control check to set the helicopter down without sustaining more damage, and without those inside making more Feats to keep from taking horrible damage in the crash. 

In short, this system is mechanically pretty simple, aligns with existing game mechanics, emulates vehicle combat as it actually happens, and increases the drama of vehicle combat quite significantly. That's all win to me.

I also think that there are opportunities to involve other characters; your engineer might be able to make a roll that the pilot fails; the pilot failed to control the helicopter as the fuel line was ruptured, but the engineer is able to manually throw the valve that stops that line. In addition, an engineer might be able to repair damage on the fly; a successful engineering check might be able to reduce damage by 1; this would be a cool mechanic to add in, meaning that a good engineer could allow your vehicle to sustain incredible damage and keep on plugging along.  Every time the engineer begins a repair, it might take 1D4 rounds (and this die will not explode). If he gets interrupted before that time is up, the repair fails. 

I'm starting to think I want to do a sourcebook for the game with expanded rules for things like vehicle combat and rules for fighting predators. I think that I've found a way to make vehicle combat feel different from front-line ground combat, which is a huge step. The next piece will be to work out fights with predators, which I was never happy with in the original rules, but I accepted it for what it was. 

This would end up replacing maybe twenty pages of existing rules with broader and more expansive rules, but would leave the vast majority of the existing rulebook intact. That seems to be a pretty solid tradeoff considering it's been a decade since the game was released.