Raymond Massey and Ruth Gordon had previously played a married couple as Abraham and Mary Lincoln in Abe Lincoln in Illinois.
A number of the writers on this picture, John Howard Lawson, A.I. Bezzerides and the uncredited Alvah Bessie were later investigated by the House of Un-American Activities Committee during the 1950s McCarthy era and blacklisted. Bessie and Lawson were listed as members of the Hollywood Ten, those pleading the First Amendment of the United States Constitution and refusing to answer questions.
A very early press release for this movie made the announcement that Edward G. Robinson and George Raft were to star in this picture.
According to A. I. Bezzerides in the book 'Screenwriter: Words Become Pictures', some of the scenes written by Hollywood Ten writer John Howard Lawson were "so out of context in their propagandistic way that the actors couldn't act them." Bezzerides cited scenes scenes involving Bogart and Julie Bishop and Raymond Massey and Ruth Gordon in particular. He went on to say that he polished every scene in the film and deserved credit, but Lawson fought against it. Bezzerides claimed that Lawson had so many friends in the Guild that he lost the arbitration and went uncredited.
According to the book 'Bill Collins presents the Golden Years of Hollywood' by Bill Collins, "For certain scenes, amazingly created on the screen, a replica of a ten thousand-ton tanker was built inside Warner Brothers sound stages six and seven. Each stage contained one half the ship's hull and deck-housing fixtures. This ship had to be torpedoed with its gasoline cargo on fire for the movie. Then a Liberty Ship was constructed on the same two sound stages for later scenes in the film. Furthermore, the size of these sets prohibited their being fixed on rocking equipment. The rocking had to come from the camera, so the camera was mounted on a crane to simulate movement!".
According to the book 'The Films of World War II' by Joe Morella, Edward Z. Epstein and John Griggs, when this movie had its premiere in New York around the 21st of May 1943, Warner Brothers mogul Jack L. Warner was presented with the Merchant Marine's Victory Flag by three hundred sailors, seventeen torpedo seamen and the US Merchant Marine band. The seamen first marched into the auditorium before the presentation. Apparently, this was "the first war pennant awarded to a member of the film industry."
According to the DVD sleeve notes, this movie was used a a recruiting film for the US Merchant Marine. They also state that the film utilized real war combat footage.
Actual German and Soviet dialogue and aircraft were used in the movie.
Apparently, the studio Warner Brothers originally planned to make just a two-reel documentary on the Merchant Marine. However, as World War II developed, this concept was changed to a feature film as there was more opportunity to incorporate dramatic action set pieces.
At the end of the movie, Humphrey Bogart says, "I'm just thinking about the trip back." This is a double entendre. On the one hand it means the voyage back home may encounter rough seas and/or weather, but there is also an interpretation relating to Russians seen rejoicing at the end of this picture. Bogart does not return their friendly advances and remains quiet and a seaman asks why. The "I'm just thinking about the trip back" line can be considered a reference to having to deal with the Russian comrades, something which is ironic considering the film does have pro-unionist and left-wing political dialogue elements in the script. This line was cut out of the movie often when it played on television in America.
Bernard Zanville's billing was changed to Dane Clark upon the theatrical release of this movie.
Director Lloyd Bacon and producer Jerry Wald were prevented from filming at sea due to the US War Department's Second World War restrictions thereby forcing the production many challenges for such exterior filming.
Director Lloyd Bacon's contract with Warner Bros. expired during production. Jack L. Warner told him, "Finish the picture and we'll talk about it," but Bacon wasn't willing to continue without a contract. Warner fired him and brought in Byron Haskin to finish the film.
Director of Phototography Ted D. McCord was replaced by cinematographer Tony Gaudio after McCord left the production to join the United States Army to fight in the Second World War. McCord doesn't have another D.O.P credit until 1945.
Near the end of the picture, as the ship is nearing Murmansk, several Russian airplanes fly out to meet them. One of the pilots keeps gunning his engine in short bursts. There are three short bursts followed by a long one. Movie audiences of the 1940s would immediately recognize this as the three dots and a dash of the Morse code "V". "V for Victory" was heavily used as a slogan during World War II.
Radio presenter Art Gilmore provides the voice of US President Franklin Delano Roosevelt at the end of this picture.
Ship-building magnate Henry J. Kaiser thought the film was a morale booster and liked the movie so much that he wanted to screen it to all his war builder colleagues and friends.
The aircraft used to attack the Sea Witch were Heinkel HE-59 biplanes.
The production shoot for this movie went forty-five days over schedule.
The whole of this movie was shot on the Warner Brothers backlot and sound stages.