Mass Combat with Surprise

 It's easy to just have armies with one number (combat strength) and smash them together. A common strategic element is that of "surprise". In Atlantis, a force with higher tactics skill gains one round of attacks with no counter-attack. This is actually pretty devastating, which has led to attempts to scale it back.

GURPS Mass Combat deals with surprise by giving the losing side a penalty to their strategy skill (they are "confused" until they can pass a strategy check). My previous post showed how critical strategy skill is to combat outcome.

I decided to measure the effect of surprise using two simple forces:

1. Force 1: One unit of medium infantry (TS 3, cost $30k)
2. Force 2: One unit of light infantry (TS 2, cost $40k)

Force 1 is stronger and cheaper. This is because light infantry have the "recon" class, which allows them to participate in the surprise calculation.

Because force 1 has zero recon, they effectively never have surprise. Force 2 will gain surprise about 60% of the time (it's random based on a quick contest of skill including strategy and intelligence gathering - 40% of the time there is no surprise).

As-is, the recon boost is clearly overpriced. Force 1 is winning about 99% of the time. Using a scaled sum, force 1 takes about $23k damage, and force 2 loses almost $40k.

I'll wait to try and balance costs until I run some more mixed force battles.

This graph shows the damage from surprise better. There is a slight shift upward in damage when surprise is gained. There's also a slight tick up in cases where force 2 can win (with heavy losses).

Or, if we just show cases where force 1 wins (and scale by the total number of battles of each case):

GURPS Mass Combat

 I am somewhat of a collector of game system rules. There are many cases where I have read rulebooks and never played the game. I have played a little GURPS, but I have read far more rules than I have ever used.

One of these is GURPS Mass Combat. GURPS is oriented towards individual action - each player has one character (PC), and is making the decisions for that character. Mass Combat is for dealing with situations where the PCs get caught up in a larger battle. It is making trade-offs between player decisions and the larger scope of army action.

As I work on a replacement for Atlantis, I wonder if the Mass Combat rules can provide a framework I can use...

I have the basic elements coded. It's interesting that force composition has probably the smallest impact on outcome - every force is reduced to one number ("troop strength"). And the ratio of the two strengths produces a modifier to the leader's strategy skill (outnumbering your opponent 1.5 to 1 gives +1 to strategy).

The biggest driver is your strategy skill. A higher strategy will allow you to dominate your opponent.

One of the nice things about making it a computer program is I can run thousands of battles in a second. I can then look at the statistics to see what is having an impact.

This is the probability distribution using the rules as written (actually, it's missing the position bonus, which will skew the numbers even worse). The forces are equally sized, with equal strategy skill levels, and choosing "simple attack" each round.

The losing force fights until elimination (100% casualties). This graph shows the damage done to the winner. The blue bars are the probability at a particular level, the red is the cumulative percentage.

The red line shows that about 50% of battles will have the winner come away with maybe 60% damage or less. And 80% of battles will give them 85% damage or less.

There is only a 5% chance of mutual annihilation.

I made one change for this graph. The rules include a -1 penalty for each 5% damage. This means that a lucky win early in the battle will cause the battle to skew rapidly toward one side. I simply removed it.

Now we see 50% of battles will result in 90% casualties for the winner. 26.5% of battles will result in mutual annihilation. No battles result with less than 60% casualties for the winner.

The rules also apply a recover of 50% casualties to the winning side. This is probably heartening for PCs who are happy to see their side win and recover - but it would be devastating in a strategy war game. A battle with equal forces could result in the utter annihilation of one side, with the winner taking 30% losses!

More data to come as I add firepower and cavalry...