I suppose I should talk about the battle sequence, then..
When a friendly unit took a shot, it would roll a die depending on the 'power' statistic. This would give a number called 'damage'. The kaiju would then try to soak the damage, and any damage left over would go through. This was pretty simple.. one die roll versus one die roll for the kaiju.
Then armour penetration would kick in, which had a different series of die rolls, generally per point of damage blocked, which would allow a certain amount to get through depending on the weapon's AP performance.
That was basically one die roll per AP grade.
Then, if damage was done, I'd have to check if it knocked out anything, which was a third die roll, compared to the 'kaiju equipment table', which was produced as part of the kaiju generation process.
I also generally kept track of range and, very loosely, battle positioning. Over time everything would try to spread out, but for the first few rounds I had to keep track of how dense everything was for possible multiple hits from the attacking kaiju. After a few turns of battle, things had time to spread out enough that range became the only important factor for that.
When kaiju attacked, they mostly followed a set of rules.. I had a couple rough rulesets for the attackers to choose from, and varied it depending on what the kaiju ended up being armed with. These changed a bit over time, and they were fun because they lead to a lot of kaiju-based screwups as they did really dumb things.
Their shots worked differently because player units had much smaller HP numbers and different kinds of protection. Some things I never quite had firmly nailed down, and were making small adjustments all the time.
What would have been nice was something to handle the 'friendly shots phase', all in one go, but it would have had to be robust enough to let me move units into and out of combat as they arrive on the battle, run out of ammo, get knocked out, etcetera. Kaiju didn't have as many weapons and I could run that part of the turn manually.
Mostly all the coders I knew were currently playing the game, so I didn't want to tell them how everything worked in sufficient detail for them to help me automate it.