Most times for a submarine to sink

In a short career of less than seven months, the US Confederate submarine the CSS H.L. Hunley sank three times. Launched in July 1863, the vessel first foundered on 29 August 1863 during a test run in which five crew were killed. After being salvaged, it sank again on 15 October 1863, killing all eight of her crew including the designer, Horace Hunley. It sank once more on 17 February 1864 during combat after deploying a 61.2-kg (135-lb) black-powder torpedo only 5 m (16 ft) of its bow, again killing all eight people on board. It was recovered for the final time from the seabed in 2000.

The H.L. Hunley was recovered quite quickly after the first two sinkings but on the third occasion, the vessel laid on the seabed for 136 years until being raised in August 2000. The submarine is now housed at the Warren Lasch Conservation Center in North Charleston, South Carolina, USA, in a special conservation tank and has been on display to the public since 2013.

Despite being arguably one of the unluckiest vessels in maritime history, the H.L. Hunley can nevertheless lay claim to some naval milestones. Before sinking itself on 17 February 1864, it successfully took out the Union Navy's USS Housatonic which was blockading Charleston Harbour, making it the first combat submarine to sink an enemy ship.