In what year did the USS Squalus sink?

The USS Squalus, a U.S. Navy submarine, sank on May 23, 1939, during a test dive off the coast of New Hampshire. This incident was significant as it led to a major rescue operation and subsequent changes in submarine safety and rescue protocols. The date is crucial in understanding the timeline of submarine history and the evolution of underwater rescue technologies. The rescue efforts from the sinking prompted advancements in submarine design, particularly regarding safety features and rescue operations, which are integral topics within undersea rescue training. Knowing the correct year helps contextualize the event within the development of naval strategy and technology.