The British Ministry of Information approached Michael Powell to make a propaganda film for them, suggesting he make "a film about mine-sweeping." Instead, Powell decided to make a different film to help sway opinions in the still-neutral United States. Said Powell, "I hoped it might scare the pants off the Americans [and thus bring them into the war]." Screenwriter Emeric Pressburger remarked, "Goebbels considered himself an expert on propaganda, but I thought I'd show him a thing or two." After persuading the British and Canadian governments, Powell started location filming in .
|Eric Portman||Lieutenant Hirth|
|Raymond Lovell||Lieutenant Kuhnecke|
|Laurence Olivier||Johnny, the trapper|
|Finlay Currie||the Factor|
|Anton Walbrook||Peter, the Hutterite leader|
|Glynis Johns||Anna, a Hutterite woman|
|Leslie Howard||Philip Armstrong Scott|
|Raymond Massey||Andy Brock|
The U-boat was built by Harry Roper of Halifax, Nova Scotia and towed to Corner Brook, Newfoundland, where it was "shot down" by the Royal Canadian Air Force in the Strait of Belle Isle at the beginning of the film. Powell forgot that Newfoundland was at the time a Crown Colony, not a part of Canada. As a result, when they moved the full-sized submarine model there, it was impounded by Customs & Excise, which demanded that import duty be paid. Powell had to appeal to the Governor of Newfoundland, citing the film's contribution to the war effort.
The "U-37" carried two 1,000 lb bombs supplied by the Canadian Air Force. Powell didn't tell the actors that they were aboard, as he thought that they might become nervous. The actors were replaced by dummies before the bombs were detonated.
Michael Powell's voice can be heard faintly in some of the submarine scenes. Once, when the camera boat almost collides with the submarine, Powell says "Keep rolling."
The men in the lifeboat at the start of the film were mainly local merchant seamen, many of whom had already been torpedoed. Lovell nearly drowned in the scene where the seaplane crashes. Even those who could swim (which Lovell couldn't) became flustered when the aircraft sank faster than anticipated. The stink bomb that was thrown in to "heighten the turmoil" added greatly to the chaos. A member of the camera crew jumped in and saved the actor.
The Hutterites near Winnipeg allowed the film company into their community. Like the better known Amish, they live in simple, self-sufficient communities, leading an austere, strict lifestyle. Elisabeth Bergner was originally cast in the role of Anna. Bergner later deserted the film, refusing to come back to England for the studio scenes. It is believed that, as an ex-German national, she feared for her life if the Nazis were to invade. Glynis Johns stepped in to replace Bergner, a rare instance of an established star standing in for a lesser-known actress. The initial long shots of Anna are of Bergner. When a Hutterite woman saw Bergner painting her nails and smoking, she became so incensed, she rushed up, knocked the cigarette from the actress's mouth and slapped her in the face. Powell had to make peace with the community and with the outraged star. For the scene where the Hutterites listen to Eric Portman's impassioned pro-Nazi speech, the actors were all "hand picked faces". Over half were refugees from Hitler.
Notable crew members include Ralph Vaughan Williams, contributing his first film score, and David Lean as editor. Raymond Massey's brother Vincent Massey, then Canadian High Commissioner to the United Kingdom, (future Governor General of Canada) read the prologue.
The British Film Institute ranked the film the 63rd most popular film with British audiences, based on cinema attendance of 9.3 million in the UK.