In the long term, several operators have announced their intention to supplement or replace their Harrier fleets with the STOVL variant of the F-35 Lightning II, designated as the F-35B.

Throughout the 1950s, particularly in the years following the Korean War, a number of aircraft companies in both Europe and America separately decided to investigate the prospective capabilities and viability of vertical take-off and landing (VTOL) aircraft, which would eliminate the requirement for vulnerable runways by taking off and landing vertically as opposed to the conventional horizontal approach.

[2] In addition to military applications, the prospect of applying such technology to commercial airliners was also viewed with considerable interest by the mid-1950s, thus the value of developing viable vertical take-off systems was judged to be substantial.

[2] Bristol's projected vectored thrust engine, which received the name Pegasus,[N 1] harnessed rotatable "cold" jets which were positioned on either side of the compressor along with a "hot" jet which was directed via a conventional central tailpipe; this concept had originated from Michel Wibault, a French aviation consultant.

[5] During the 1960s, the P.1127 attracted the attention of the RAF; this would eventually result in the development and issuing of Requirement ASR 384, which sought a V/STOL aircraft for ground attack operations.

[7] Around the same time as the RAF's interest in the concept, NATO proceeded to develop their own specification, NBMR-3, which called for a vertical takeoff and landing (VTOL) aircraft; specific requirements included the expectation for the performance of such an aircraft to be equivalent to the conventional McDonnell Douglas F-4 Phantom II fighter.

The first version entered service with the Royal Navy's Fleet Air Arm in April 1980 as the Sea Harrier FRS.1, and was informally known as the Shar.

[19][20] Wartime experiences led to the production of an improved model in the form of the upgraded Sea Harrier FA2; this version entered operational service on 2 April 1993.

[23] As early as 1973, Hawker Siddeley and American aviation manufacturer McDonnell Douglas were jointly working on development of a more capable version of the Harrier.

[24] The Harrier was extensively redeveloped by McDonnell Douglas, and later joined by British Aerospace (now parts of Boeing and BAE Systems, respectively), leading to the family of second-generation V/STOL jet multi-role aircraft.

[26][27] The RAF also chose to procure the second generation of the British Aerospace-built (with McDonnell Douglas as subcontractor) Harrier II GR5/GR7/GR9, which entered service in the mid-1980s.

Landings are not usually done in a conventional manner because the range of speeds at which this is advisable is narrow due to the relatively vulnerable outrigger undercarriage.

Rotating the vectored thrust nozzles to some angle other than rearwards during normal flight (to a maximum of 8-degree forward of vertical, i.e. 98 deg.)

Thrust from the engine can be temporarily syphoned to control the aircraft's pitch, roll and yaw before it is going fast enough for the elevators, rudder and ailerons to become effective.

Accelerating and decelerating transitions between hovering and conventional flight required considerable skill and concentration on the part of the pilot, especially in crosswind conditions.

On two occasions the Royal Air Force explored whether experienced helicopter pilots, with their ability to hover and transition to forward flight, would be a better source for Harrier squadrons.

In both cases the pilots were completely out of their depth with conventional flight, navigation, orientation and weapons delivery at the high speeds of a fast jet.

Pilots were impressed that to control the aircraft's vertical flight required only a single lever added in the cockpit.

[48] In June 2011, the MoD denied press reports that the aircraft were to be sold to the US Marine Corps for spares to support their AV-8B fleet.

The two systems are fully interlinked but air is not supplied to the reaction control valves during conventional wingborne flight.