The Ultra Simplified GURPS Combat System You Probably Don't Know About

Are you a person who wishes there was a way to run combat in GURPS that was super simple? One even simpler than the Combat Lite chapter of GURPS Characters (pp, B324-328)? What if I told you this system exists in an often overlooked GURPS book and that even if you are aware of it, you might have missed that you could just use it as the combat system?

This system is BATTLE from GURPS Action 7: Mercenaries (pp 7-9). BATTLE (Basic ATTack resoLution systEm) is ostensibly for quickly resolving war movie inspired skirmishes for a player mercenary company, but what it really is a system for resolving combat with just one roll per player character plus one additional roll for the team leader. It can easily be scaled down to just the five-man band player character party and modified to fit any TL or setting.

While it can be used as-is, with some imagination, some modifications may help it run smoother at a smaller scale:

Relative Numbers and Other Asymmetries 

As written BATTLE doesn't take into account which side is larger, stronger, in a better position etc. This is all abstracted into BAD and Combat Zone BAD. If you want to have these things matter consider giving the ratio (rounded down) in numbers as bonus to the larger side's BATTLE roll, up to +5. Each condition that gives an advantage, e.g. fortified position can give +1, or +2 if the GM rules it an especially  significant advantage. 

Casualties

Mercenaries p.9  says you should:

feel free to interpret casualties as loosely as necessary to create drama and fun.

 This works, at any scale, but if you want to do something more systematic consider the following:

1. Add up all the PC's (and any NPC allies, dependents, hirelings etc. that are potentially exposed to combat) HP. Record this and use it for all battles unless something changes.

2. Apply the percentage from the BATTLE Table (p.7) to that total (round up).

3. If any PCs failed their Complementary skill roll, assign this result as injury between these PCs. You can either have the players chose how to distribute it, have the GM do it arbitrarily, or divide it as evenly as possible, assigning the highest amount to the fighter with the largest margin of failure.

4. If no PC failed, then distribute this injury amongst the entire party and followers. You can divide it evenly as well; assigning the largest damage to the smallest margin of success.

For enemies it's probably easiest to just apply the percentages directly to their numbers.

Example: The party's total HP is 59. They win a battle by a margin of 5, giving 10% casualties, but two players failed their skill rolls. These characters take six injury split between them. 

Variations

More Lethality: The above doesn't directly take into account that in GURPS HP can be negative. If you desire more lethal fights multiply the total in step 1 by 2 (or more).

Even More Lethality for More Simplicity: Alternately you can just apply the percentage directly to the PC's numbers. E.g. if a party of five take 50% casualties, this means that two of them are dead, unconscious, seriously crippled or otherwise hors d'combat and one has a Major Wound, is at 1/3 HP or a similar partially wounded state.

Hit Locations: You can roll random hit location when assigning this injury, potentially crippling limbs.

Flesh Wounds: Utilizing any of these methods, consider allowing PCs to spend 1 character point to reduce their injury to 1 HP.

Subsequent Battles

Mercenaries p. 7 says to apply the margin of success on the previous BATTLE roll to the next one, and Climactic Batttles p. 8 suggests fighting 1d/2 +1 per -1 BAD battles before a climatic battle (using normal GURPS Action rules). In other kinds of adventures this may still apply. For example in a dungeon delving game, you may have combat encounters in rooms and from wandering monsters, and a final boss fight. In this case you have as many battles as the party encounters before the boss, but still have the margin of success carry over from the previous battle (representing the delver's and the denizens' morale and resources). In a monster hunt you may have the PCs encounter the monster 1d/2 +1 per -1 BAD times, inflicting some damage (based on the BATTLE table results) each time, with margin of success influencing the next roll, leading up to the final confrontation.

Opportunities and Challenges

The Opportunities Table and Challenges Table (both p.8) assume a TL6-8 battlefield environment. You can interpret the results in a way appropriate to your setting (e.g. a "vehicle" result might instead be an armored knight or a huge troll), make your own appropriate tables, or just not use these optional rolls at all.

The Fight Scene

The box on p. 7 suggests you narrate a montage of each player's fight scenes. Some people may not like this, and it can add extra time. It's not actually required, though. The only important thing is that the player rolls their complementary skill roll, they don't even need to explain how their skill is relevant if you don't want this level of detail.

Even Less Rolling

You could not even have the PC's roll individual complementary skills, but just automatically assume +1 per player character, resolving every combat encounter with one roll.