The Sinking of USS Housatonic on 17 February 1864 during the American Civil War was an important turning point in naval warfare.

Hunley approached just under the surface, avoiding detection until the last moments, then embedded and remotely detonated a spar torpedo that rapidly sank the 1,240 long tons (1,260 t) sloop-of-war with the loss of five Union sailors.

Housatonic was a 1,240-long-ton (1,260 t) vessel with an armament of twelve large cannons, stationed at the entrance of Charleston Harbor roughly five miles (8.0 km) off the coast.

Hunley began her approach at about 8:45 pm, commanded by First Lieutenant George E. Dixon and crewed by seven volunteers.

Five men – two officers and three crewmen – went down with their ship while an unknown number of Union Navy sailors were injured.

Hunley won her first victory, but was lost at sea the same night while returning home to Sullivan's Island.

Hunley was sunk as the result of her own torpedo exploding, but some claim that she survived as long as an hour after destroying Housatonic.

However, a team of historians managed to examine the submarine's remains, and theorized that a crewman on Housatonic was able to fire a rifle round into one of H.L.

Hunley was less than 20 feet (6.1 m) away from the point of detonation – much closer than previously realized – and thus the explosion probably damaged the submarine as well as its target, although it was impossible to tell at the time due to concretion covering the hull.

[11][12] Later studies showed that the crew was probably instantly killed through blast injury caused by the close proximity of the torpedo, though this remains disputed.