·Director Robert Aldrich wanted to obtain the right to adapt before EMNathanson's novel of the same name was formed, but in the end Metro-Goldwyn-Mayer Inc. successfully obtained the right to adapt in 1963. The novel was published in 1965 and became a bestseller that year.
·The French castle in the film was specially built for the filming. A total of 85 craftsmen were used. It spans 240 feet and is 50 feet high, making it one of the largest film sets. The gardener planted 5,400 square yards of heather, 400 ferns, 450 shrubs and 6 weeping willows around it.
·According to the plot, the castle will be blown up, but the castle is so strong that it requires 70 tons of explosives, and part of the castle needs to be rebuilt with cork and plastic.
John Wayne was the original candidate to play Major John Lissman, but he gave up because he wanted to star in "Green Beret" in 1968.
·The actors Lee Marvin, Telly Savalas, Charles Bronson, Ernest Borgnine, and Clint Walker all served during World War II.
Donald Sutherland was the last actor to be determined because the original actor believed that the role he was going to play was detrimental to his image.
Director Robert Aldrich said that cutting off a shot of Robert throwing a grenade into the air-raid shelter would give him the Academy Award for Best Directing . This shot is controversial because no German women survived in the air-raid shelter.
Jack Palance refused to play the role of Archer.
·Because Trini López's agent blindly asked for higher pay, director Robert Aldrich let his role die early.
