An aircraft catapult is a device used to launch aircraft from ships, most commonly used on aircraft carriers, as a form of assisted take off. It consists of a track built into the flight deck, below which is a large piston or shuttle that is attached through the track to the nose gear of the aircraft, or in some cases a wire rope, called a catapult bridle, is attached to the aircraft and the catapult shuttle. There have been different means of which have been used to propel the catapult, such as weight and derrick, gunpowder, flywheel, air pressure, hydraulic, steam power, and also in development to use electromagnets.