Theodore Bikel speaks only Russian in the film. Norman Jewison has acknowledged that Bikel's knowledge of the language was a principal reason in casting him.
Ordinary townspeople were used as extras in the film. They were so thrilled to be a part of production that the rushes were shown at the end of each day in a local theater. The townspeople went every night, bringing their entire families with them.
Unable to borrow a real submarine from the US Navy and unable to bring a Soviet submarine to the United States, the art department built the Russian sub. It is powered by four motors underneath the hull, each driving a section of the "sub". It can be seen flexing where the four sections are joined.
Norman Jewison said that the reason he wanted Carl Reiner as the star was his belief that audiences would more readily accept the character as a writer if he were played by an actor that was known to also be a writer.
The story is based on "The Off-Islanders", a novel by Nathaniel Benchley. Nathaniel Benchley is the son of humorist and actor Robert Benchley and the father of Peter Benchley who wrote the novel "Jaws".