The Mind Snatchers

James Reese is a U.S. soldier stationed in Europe whose violent temper has sent him to the stockade several times. He is surprised one day to be driven to a remote hospital facility and checked into a room with another soldier named Miles. James learns that his roommate also has spells of aggressive behavior, and after witnessing one of these outbursts, Miles is taken away and returns with a new, docile personality. James eventually learns that the army is experimenting with a new brain operation that alters aggressive personalities and to his horror, realizes that he is the next guinea pig. (official distributor synopsis)