Human torpedoes or manned torpedoes are a type of rideable submarine
used as secret naval weapons in World War II. The basic design is
still in use today as a type of diver propulsion vehicle.
The first human torpedo was the Italian Maiale ("Pig"). It was
electrically propelled, with two crewmen in diving suits riding
astride. They steered the torpedo at slow speed to the enemy ship.
The detachable warhead was then used as a limpet mine. They then
rode the torpedo away.
In operation, the Maiale torpedo was carried by another vessel
(usually a normal 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.
The idea was successfully applied by the Italian navy (Regia Marina)
early in World War II and then copied by the British when they
discovered how powerful this new weapon was after three Italian
SLC's successfully forced the harbour of Alexandria and damaged the
two British battleships HMS Queen Elizabeth and HMS Valiant, and the
tanker "Sagona." The official Italian name for their craft was "Siluro
a Lenta Corsa" (SLC or "Slow-running torpedo"), but the Italian
operators nicknamed it "Maiale" after their inventor Teseo Tesei
angrily called it a pig when it had been difficult to steer. The
British copies were named "chariots".