A torpedo is an underwater missile in the shape of a cigar that can be launched from a ship, submarine, or dropped from an aircraft and explodes when it reaches its target. A modern torpedo is an advanced underwater ranged weapon that is launched above or below the water's surface, is self-propelled, and has an explosive warhead that will go off either when it makes contact with the target or is close by.

Historically, simple naval mines were also referred to as torpedoes. Up to the late 19th century, these were utilized on an as-needed basis during the early modern era. Cornelius Drebbel, a Dutchman working for King James I of England, invented the first spar torpedoes. He placed explosives to the end of a beam attached to one of his submarines, and they were utilized (with little success) during the English expeditions to La Rochelle in 1626. 

Torpedoes have to be given better warheads and motors due to increased submarine strength and speed. With the development of nuclear-powered submarines during the Cold War, which did not frequently have to surface, especially those carrying strategic nuclear missiles, torpedoes became a valuable tool.