The tug used in this movie was H.M.S. Restive (HMT W 39), a Royal Navy Rescue Tug of the Assurance class. This class of tugs was built between 1940 and 1943. With a 1,350 horsepower engine, these tugs could make fourteen knots and were powerful enough to haul just about any capital ship back to port. Five (out of twenty-one built) were lost during the war. The ship numbers used in this movie (W 83, W 86 and W 88) were not used by any ship of this class during the war.
Two endings were shot according to tcm.com. One had David join Stella on the train, the other had him just miss it, but promising to find her. This was apparently to satisfy the Motion Picture Production Code since the characters were not married.
After just a few weeks of filming, writer and producer Carl Foreman wanted to replace Sophia Loren with Ingrid Bergman but William Holden persuaded Foreman to keep her.
Hairy chested William Holden was once again required to undergo a complete torso wax for his singular, abbreviated shirtless scene, but Kieron Moore was allowed to retain his natural foliage for his.
A wall calendar establishes the time of the story as January 1941. Tuesdays and Fridays are in lighter type to represent Meatless Days, a World War II rationing provision. By the time this movie ends, the U.S. has entered the war, and Christmas 1941 is celebrated amidst the bombing.