Michael Goodliffe, who plays Capt. Stein, was an actual Prisoner of War during WWII. He was captured at Dunkirk and spent the next five years in a German POW camp.
The leather jacket that Frank Sinatra wore was later worn by Bob Crane in Hogan's Heroes (1965). It was later worn by Greg Kinnear in Auto Focus (2002).
The author of the book, David Westheimer, was a navigator on a B-24 that was shot down over Italy in WWII, and he was a POW in Stalag Luft III. Westheimer had witnessed the bombing of Bolzano in 1943 from a box car.
The crew was flown back to Hollywood at great expense when studio head Richard D. Zanuck decided to have the Italian POW camp constructed in California. It also would be used for an episode of Voyage to the Bottom of the Sea (1964).
Adolfo Celi, who plays Major Battaglia, became somewhat iconic that same year playing the one-eyed villain Largo in the James Bond film, Thunderball (1965).