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. This was the famous duo's first meeting, though it would be months before their romance began.
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, which many of this film's key players were a part. Some "usual suspects" include director Michael Curtiz, stars Humphrey Bogart and Claude Rains, supporting and bit players Peter Lorre, Sydney Greenstreet, Helmut Dantine and 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, Michèle Morgan was originally cast as Ilsa in "Casablanca", but her salary demand was too big, so Ingrid Bergman was cast instead.
The plane shown attacking the freighter is an accurate model of a Focke-Wulf 200 (except for the fact that it was shown to have a bomb bay, which it didn't have), a bomber developed from a airliner.
Warner Bros. built a full-scale Merchant Marine ship in three months, modeled after the French ship Ville de Nancy.