When a train construction project is completed, it gets the offensive spawns (which includes a golem on trains-4 and higher) but also a superfortress to put on a planet of its choosing (though it can't put it on a planet that already has a superfort).
That's just how it shows that it cares
Hmm. Isn't that a bit overpowered? How can I win without super weapons now?
Well, how would you beat a Fortress Baron (not Fortress King) AI? They get a number of superforts (on an 80 planet map, a single Fortress Baron AI will get 5 superforts on diff 7, and 7 on diff 10).
How often are the train construction events happening for you, and on what intensity are the trains?
I'm not saying it's balanced now, it was just a first try, but I need to know what's actually going on in your situation.