I’m not sure I’ve ever heard of a locomotive being used as a weapon. Maybe a more apt comparison would be “nuclear fission invented nuclear fallout”, no?
Intentional derailment is something that has happened which feels closer to the example then using the train itself as a weapon IMHO. https://en.wikipedia.org/wiki/Battle_of_Mill for example
railway guns go all the way back to the us civil war, but i suppose we can still quibble on locomotive there.