There are four main versions of the Harrier family: Hawker Siddeley Harrier, British Aerospace Sea Harrier, Boeing/BAE Systems AV-8B Harrier II, and BAE Systems/Boeing Harrier II. The Hawker Siddeley Harrier is the first generation version and is also known as the AV-8A Harrier. The Sea Harrier is a Maritime strike/air defence fighter. The AV-8B is the second generation Harrier and the BAE Harrier II is the British variant of the second generation Harrier.
VTOL (Vertical Take-Off and Landing)
VTOL is an abbreviation for Vertical Take-Off and Landing aircraft. This classification includes fixed-wing aircraft that can hover and take off and land vertically, helicopters, and other aircraft with powered rotors, such as tiltrotors. Autogyros, balloons, airships and rockets are not normally considered VTOL. Some VTOL aircraft can operate in other modes as well, such as CTOL (Conventional Take-off and Landing), STOL (Short Take-Off and Landing), and/or STOVL (Short Take-Off and Vertical Landing) mode. Others, such as some helicopters, can only operate by VTOL, due to the aircraft lacking landing gear that can handle horizontal motion. VTOL is a subset of V/STOL.
Besides the ubiquitous helicopter, there are currently two types of VTOL aircraft in military service: craft using a tiltrotor, such as the Bell Boeing V-22 Osprey, and aircraft using directed jet thrust such as the Harrier family.