The Colonial Marines cast was a mix of British and American actors who underwent three weeks of intensive training with the British Special Air Service (SAS). Vietnam War veteran Al Matthews (Apone) helped to train the actors, teaching them not to point their weapons at people because their blanks were still hazardous. The training was intended to help the marine cast to develop camaraderie and treat the rest of the cast (Weaver, Reiser, and Hope) as outsiders. Biehn's late casting caused him to miss the training, and he said he regretted being unable to customize his armor like the other actors had (since he inherited Remar's). Cameron created a backstory for each marine.