John Wayne said he believed the extremely negative reviews probably helped the film's box-office performance. He further said that he felt critics were attacking the war itself rather than his film.
John Wayne's character, Col. Mike Kirby, is based on the real-life Lauri Törni, who later on called himself Larry Thorne. He was a Finnish army captain who fought in the Second World War during the Winter War (1939-40) and Continuation War (1941-44) against the Soviet Union. He served on the Eastern Front as a Waffen-SS captain (under the alias Larry Lane) of the Finnish Volunteer Battalion of the Waffen-SS. He emigrated to the U.S. in the late 1940s and in 1954 joined the U.S. Army. In November 1963 he joined Special Forces unit A-734 in Vietnam and fought in the Mekong Delta. He disappeared during a mission in 1965 and was reported MIA (Missing In Action). His remains were found in 1999, and formally identified in 2003. He is the only former Waffen SS member buried in Arlington Nation Cemetery.
Aldo Ray's alcoholism was a continual problem during filming, to the extent that John Wayne had to give some of Ray's dialogue to other characters.
At the beginning of filming George Takei told John Wayne he was strongly against the Vietnam War. Wayne replied that so was half of the cast and crew, and that he had hired Takei for his acting ability and not for his political views.
Jim Hutton was against the U.S. involvement in the Vietnam War, although his involvement in this film caused many to mistakenly believe he shared John Wayne's pro-war views.