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.
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.
John Hoyt, Whit Bissell, and George Takei all went on to become legendary television actors of the 1960s, and all three played memorable roles in Star Trek (1966), but no two of them, let alone all three, were ever in the same episode of that show.