During filming, Lauren Bacall was brought to the set in order to gauge her chemistry with Humphrey Bogart, with whom she would soon be co-starring in To Have and Have Not (1944). This was the famous duo's first meeting, though it would be months before their romance began.
Warner Bros. built a full-scale Merchant Marine ship in three months, modeled after the French ship Ville de Nancy.
One of the few films to employ a flashback within a flashback within a flashback. This film is often seen as an attempt to recapture the magic of Casablanca (1942), in which many of this film's key players were a part. Some of the "usual suspects" include director Michael Curtiz, stars Humphrey Bogart and Claude Rains, supporting and bit players Peter Lorre, Sydney Greenstreet, Helmut Dantine, Corinna Mura, writer Casey Robinson, composer Max Steiner, producer Hal B. Wallis and executive producer Jack L. Warner. (Both films were made by Warner Bros.) Also, co-star Michèle Morgan was originally cast as Ilsa in "Casablanca", but her salary demand was too high, so Ingrid Bergman was cast instead.
According to the film's editor, Don Siegel, when Hal B. Wallis asked him what he thought of the movie, Siegel questioned the use of numerous flashbacks. Wallis never forgave him.
In a scene in the prison, just before the breakout, the camera pans across the bunks of the prisoners. Renault, one of the five who ends up escaping, is shown making something with small pieces of wood. An easily missed detail is that he is making a miniature model of a guillotine.