Setup an attack value (+0 to +5) for vs fast, vs long range, vs large target, vs heavily armored, vs air, vs sea, vs under water, vs land, and vs troops.
Give each unit a defense of "attacked by fast," "attacked at long rage" etc.
Give each unit a rough health, 1-10.
Give each unit a rough range (blocks, maybe make each block a mile? Less?). Position forces.
Figure out a "turn order," roughly. Add in random.
Each unit attacks by rolling the most appropriate two checks. Each unit defends by countering with the two corresponding checks. The difference between the two are the damage value…