Even though the beginning and the end of the film occur in the port of La Rochelle, it does not correspond historically. The submarine base in La Rochelle was not functional before November 1941, and at the time of the film the port was dried up. While Saint-Nazaire was the base used in the novel and where "U-96" was based at in late 1941, the film was changed to La Rochelle because its appearance had not changed to such a large degree in the years since World War II. Moreover, none of the British fighter-bombers of late 1941 to early 1942 had the range to bomb La Rochelle from bases in the U.K.; however, it is possible the fighters were carrier-based and not land based.