I think this film is from 70's or 80's. I remember this much. A guy is notified that his brother (soldier) is dead. The guy goes to the base where his brother was stationed and finds that the military base has been taken over by an intelligent but malevolent alien flying craft which controls the soldiers there. The alien flying craft builds a huge robot body for itself (and sits atop the giant body). In the climax battle, the guy and a military General kill the alien with a bazooka or rocket launcher. Any ideas ? Thanks.

INVADER (1992) (http://www.youtube.com/watch?v=EltAwwGhc9Y)?

You found it, Adolf ! Thanks.