Steve McQueen's role was originally going to be played by Sammy Davis Jr.. A feud had broken out between Davis and Frank Sinatra after Davis had claimed in a radio interview that he was a greater singer than Sinatra. Sinatra demanded he be dropped from the cast, and McQueen got the part.
According to the Australian DVD sleeve notes, this was Italian Gina Lollobrigida's first movie that she made in Hollywood.
This movie is based on the real-life story of World War II's OSS Detachment 101. This was an OSS Operations Group designed to specialize in activities in the China-Burma-India region in collaboration with the Kachin Rangers and other Allied special operations units.