The Rolls-Royce Pegasus is a turbofan

Turbofan

The turbofan is a type of airbreathing jet engine that is widely used for aircraft propulsion. A turbofan combines two types of engines, the turbo portion which is a conventional gas turbine engine, and the fan, a propeller-like ducted fan...

 engine originally designed by Bristol Siddeley

Bristol Siddeley

Bristol Siddeley Engines Ltd was a British aero engine manufacturer. The company was formed in 1959 by a merger of Bristol Aero-Engines Limited and Armstrong Siddeley Motors Limited. In 1961 the company was expanded by the purchase of the de Havilland Engine Company and the engine division of...

, and now manufactured by Rolls-Royce plc

Rolls-Royce plc

Rolls-Royce Group plc is a global power systems company headquartered in the City of Westminster, London, United Kingdom. It is the world’s second-largest maker of aircraft engines , and also has major businesses in the marine propulsion and energy sectors. Through its defence-related activities...

. This engine is able to direct thrust

Thrust

Thrust is a reaction force described quantitatively by Newton's second and third laws. When a system expels or accelerates mass in one direction the accelerated mass will cause a force of equal magnitude but opposite direction on that system....

 downwards which can then be swivelled to power a jet aircraft

Jet aircraft

A jet aircraft is an aircraft propelled by jet engines. Jet aircraft generally fly much faster than propeller-powered aircraft and at higher altitudes – as high as . At these altitudes, jet engines achieve maximum efficiency over long distances. The engines in propeller-powered aircraft...

 forward. Lightly loaded, it can also manoeuvre like a helicopter

Helicopter

A helicopter is a type of rotorcraft in which lift and thrust are supplied by one or more engine-driven rotors. This allows the helicopter to take off and land vertically, to hover, and to fly forwards, backwards, and laterally...

, vertically for takeoff and landings. In US service, the engine is designated F402.

The unique Pegasus engine powers all versions of the Harrier family

Harrier Jump Jet

The Harrier, informally referred to as the Jump Jet, is a family of British-designed military jet aircraft capable of vertical/short takeoff and landing operations...

 of multi-role military aircraft

Military aircraft

A military aircraft is any fixed-wing or rotary-wing aircraft that is operated by a legal or insurrectionary armed service of any type. Military aircraft can be either combat or non-combat:...

.