Sir! No Sir! is a documentary produced, and written by David Zeiger about the opposition to the Viet Nam War in military ranks. Subtitled “the suppressed story of the GI movement to end the war in Vietnam,” it won the audience award at the Los Angeles Film Festival and the Golden Starfish Award for best documentary in 2005.
It consists in part of interviews with Vietnam veterans explaining the reasons they protested the war. According to Pentagon figures, between 1966 and 1971 there were over 500,000 incidents of desertion in the U.S. military.
I am adding this one to my list of recommended documentaries.