Both Lee Marvin and Toshirô Mifune actually served in the Pacific during World War II, of course on opposing sides. Marvin was a US Marine. He was wounded during the war and received the Purple Heart during the Battle of Saipan in 1944. Mifune served in the Imperial Japanese Army Air Service.
After the producers changed the original ending without consulting him, director Sir John Boorman vowed to always retain creative control of his projects from then on.
The movie had one of the more expensive productions at the time. This, combined with the movie's unusual concept, lack of subtitles and unpopular ending, caused the movie to become one of the biggest box office bombs of its time. It lost some four million dollars, which was one of the factors that caused its production company, ABC films (subsidiary of the ABC company), to eventually go bankrupt. However, the critics did praise many aspects of the film, especially Toshiro Mifune's performance as one of the best in his career.
This began filming as " The Enemy is War "
Shinobu Hashimoto was brought on to inject an authentic voice to the Japanese dialogue. However, his rewrite to the script made Toshirô Mifune's character a buffoon which in turn would have made the film a comedy. Mifune refused to play the character any other way than how Hashimoto wrote it. After a series of back-and-forth battles with his interpreter, director Sir John Boorman convinced Mifune that the version of the script by Hashimoto was in error.