Human torpedoes or manned torpedoes are a type of diver propulsion vehicle on which the diver rides, generally in a seated position behind a fairing. They were used as secret naval weapons in World War II. The basic concept is still in use. The name was commonly used to refer to the weapons that Italy, and later (with a larger version) Britain, deployed in the Mediterranean and used to attack ships in enemy harbors. The human torpedo concept has occasionally been used by recreational divers, although this use is closer to midget submarines. History of common wartime models The concept of a small, manned submarine carrying a bomb was developed and patented by a British naval officer in 1909, but was never used during the First World War. The Italian Navy experimented with a primitive tiny sub (Mignatta) carrying two men and a limpet mine: this craft successfully sank Austro-Hungarian battleship SMS Viribus Unitis on 1 November 1918. The first truly practical human torpedo was the Italian Maiale (nicknamed the "pig" because it was difficult to steer) used in the Second World War. The Maiale was electrically propelled by a motor in most of the units manufactured, with a top speed of and often required a travel time of up to two hours to its target. Two crewmen in diving suits rode astride, each equipped with an oxygen rebreather apparatus. They steered the craft to the enemy ship. The "pig" could be submerged to , and hypothetically to , when necessary. On arrival at the target, the detachable warhead was released for use as a limpet mine. If they were not detected, the operators then rode the mini sub away to safety. Development began in 1935 but the first 11 were not completed until 1939 by San Bartolomeo Torpedo Workshops in La Spezia, Italy and a larger number followed. The official Italian name for the majority of the craft that were manufactured was Siluro a Lenta Corsa (SLC or "Slow-running torpedo"). Two distinct models were made, Series 100 and then (in 1942) Series 200 with some improvements. At least 50 SLCs were built by September 1943. In operation, the Maiale torpedo was carried by another vessel (usually a conventional submarine), and launched near the target. Most manned torpedo operations were at night and during the new moon to cut down the risk of being seen. Attacks in 1940 were unsuccessful