Yep there was a cinematic in sc1 where a group of marines plant a nuke in a science vessel. I also think some of the indoor mission were played in one of them. So yeah, they're pretty big.
Amazing. But this kind of bothered me: Hey guys, there's this giant thing floating in the sky. Let's send a few Vikings to piss it off and have a couple of marines and a tank patrolling the streets just in case. When shit does hit the fan let's all stand in a line and meet them in the open. Like, no bunkers? maybe a Thor…