The loss of the submarine ARA San Juan this past November is the most significant loss of a submarine since an explosion sank the Russian Oscar-class nuclear-powered guided-missile submarine Kursk in 2000. All 44 sailors aboard the German-designed Type 209 diesel-electric submarine were lost when it went on eternal patrol.
It took over four months, but the story of what happened to the San Juan was finally revealed in August of 2018. According to a report by TeleSurTV.com, the submarine suffered a fire in her forward battery compartment on Nov. 15, 2017, after seawater went down the submarine's "snorkel."
The crew of the sub fought the fire for two hours as the submarine descended. The vessel then reportedly imploded, instantly killing all 44 sailors on board. Claims that the submarine was in poor material condition were denied by the Argentinean Navy. A massive rescue effort, which included a Lockheed P-3 Orion and a Boeing P-8 Poseidon from the United States Navy, went on for weeks before the search was called off.
In the years after World War II, the United States lost two Balao-class diesel-electric submarines. In 1949, USS Cochino (SS 345) suffered a pair of battery explosions that sank the ship despite a 14-hour effort to save the vessel. One civilian engineer on the Cochino and six sailors from USS Tusk were lost.
In 1958, USS Stickleback (SS 415) was taking part in a training exercise when she lost power, broached the surface, and was rammed by the John C. Butler-class destroyer escort USS Silverstein (DE 534). Efforts by the crews of both vessels, plus the submarine USS Sabalo (SS 302), the destroyer escort USS Sturtevant (DE 239), and the submarine rescue ship USS Greenlet (ASR 10) to save the Stickleback failed. The sub sank, but all aboard were rescued.