on the mission where you are with the marines (semper fi or die) after the flood and the ceph pods are landing all around you...there is a tactical option that says destroy on a subway car hovering over the battlefield. I've shot everything i see and it wont blow up.

I think a ceph gunship should blow open a wall. So, you and marines can go inside the building. I encounter a script problem when the gunship
doesn't show up and have to restart the level from the beginning.

no i'm past that part. this is an optional way to kill the ceph by somehow dropping the train onto their heads. ...not sure how to dislodge it

i think there was an explosive gas can inside or something if I remember that you can shoot.