The USS Squalus (SS-192), a Sargo-class submarine of the United States Navy, was conducting a test dive off the coast of New Hampshire on 23 May 1939. During this maneuver, a valve malfunction led to water flooding the vessel, causing it to sink at a depth of approximately 240 feet. In total, 24 sailors and two civilian technicians were killed due to the mishap. The remaining crew members, 32 sailors and one civilian naval architect, were able to escape into the forward torpedo compartment and awaited rescue while trapped in the submerged submarine.

Rescue efforts commenced immediately. The U.S. Navy utilized the McCann Rescue Chamber, an innovative rescue device designed to retrieve submariners stuck in sunken vessels. After complex rescue operations, the trapped sailors were successfully brought to the surface the next day, amidst a highly publicized and intense operation. The rescue mission was noteworthy for its technical sophistication and the challenges faced in coordinating rescues at such depths.

In the aftermath of the sinking, investigations were conducted to determine the precise cause of the incident. The USS Squalus was later salvaged and underwent repairs before being recommissioned as USS Sailfish (SS-192). The event significantly influenced submarine safety measures and led to an increased focus on mechanical reliability and crew training in the U.S. Navy.