The other sub seen at Panama marked "P3" is the U.S.S. Shark (SS-174). She was built by the Electric Boat Company at Groton, CT and commissioned in 1936. Her home port was at San Diego from 1937 to 1940 when she joined the Asiatic Fleet based at Manila, Philippines. She was the first U.S. submarine lost to enemy anti-submarine action in WWII when, according to post-war Japanese records, a destroyer sank a surfaced sub on February 11, 1942. Reported as "presumed lost" on March 7, 1942, she was struck from the Naval Register on June 24, 1942. In a curious turn, the Japanese destroyer which probably sunk the U.S.S. Shark was the IJN Yamakaze which was in turn sunk by the U.S.S. Nautilus (SS-168) - the sub marked "N2" in this film - on June 25, 1942.
The U.S. Navy and the submarine base at New London, Connecticut, had to approve the story to protect military secrets.
The submarine "D-1" in the film was the U.S.S. Dolphin (SS-169). She was commissioned at the Portsmouth Naval Shipyard in 1932 and then moved to San Diego where she was home-ported at the time of this film. During WWII she performed three war patrols from 1941 to 1942, then served as a training sub out of Pearl Harbor until 1944. She was moved to the sub base at New London, CT and served as a school boat until being decommissioned in October, 1945 and sold for scrap in August, 1946.
Sock and Lucky discuss the naval exercise they are taking part in named "Fleet Problem 20." They are really talking about Fleet Problem XVII which took place in 1936, which pitted the U.S. Navy's main surface battle fleet against the Scouting Force, a smaller unit consisting of older ships and the Navy's submarine fleet. The Fleet Problem XX would not occur until February, 1939.
The rescue ship shown in the first part of the film is the U.S.S. Falcon (ASR-2). Originally commissioned as a minesweeper in 1918, she was converted to a submarine rescue ship in 1929. During WWII she was a training ship for divers and sailors on newer ASRs, and was the flagship for the commander of the Atlantic submarine fleet. She was decommissioned in 1946 and sold for scrap in 1947.