Hands down one of the most revolutionary designs in aviation history, the Hawker Siddeley Harrier was the world's first Vertical/Short Takeoff or Landing (V/STOL) combat aircraft to enter service. It's origins lay in the 1957 Hawker P.1127 prototype which used engines with movable nozzles to provide the necessary vectored thrust for taking off and landing vertically. Shortly after entering service in the RAF in the 1970s, the USMC found in the Harrier an ideal aircraft for the support of amphibious assaults from helicopter carriers, and operations in hastily-prepared landing sites. Over one hundred AV-8 Harriers were purchased directly and were eventually fitted with a number of US avionics though were otherwise almost identical to their RAF counterparts. Partnership between McDonnell Douglas and British Aerospace led to further improvements in the design and the next generation of Harrier aircraft, known as the Harrier II, were produced separately in the UK and the US for each country's particular requirements though with the same primary ground-attack role, with some secondary air-to-air capability that benefited from the aircraft's ability to use vectoring while in flight. During the Gulf War, AV-8s proved their versatility by being the aircraft which were deployed closest to the Kuwaiti border, barely 40 nautical miles behind the lines. USMC Harriers have been seen in combat in nearly every other conflict involving US forces since then, and can employ a number of sophisticated smart bombs, stand-off missiles, and targeting pods. Unlike the RAF and RN which have phased out their Harriers, the aircraft remains in service with the USMC but is being gradually replaced with the V/STOL-capable F-35B. Harrier IIs based on US versions are in use with the Spanish and Italian navies, serving on board their respective V/STOL carriers.

Initial delivery of the first batch of British-made Harriers was done in January 1971, these were designated AV-8A in US service. These were almost identical to the RAF's GR.1 variant, but they were later given an airframe life extension plus new avionics and redesignated AV-8C. The second major update resulted in the AV-8B Harrier II, a true collaborative effort between McDonnell Douglas and British Aerospace and which roughly corresponds with the RAF's GR.5, albeit with different avionics and equipment, gun pod, and some other minor airframe differences (notably one less pair of pylons). The AV-8B was later upgraded with night-attack capability (similar to the RAF's GR.7) though the designation remained the same. Finally, an AN/APG-65 radar was incorporated into the AV-8B Harrier II Plus which also came with a redesigned cockpit. Two-seat trainer variants are known as the TAV-8A and TAV-8B for both the Harrier and Harrier II respectively. Both Italian and Spanish Harrier IIs correspond with standard AV-8B and Plus versions (Spanish versions are designated EAV-8B Matador II). Unlike USMC versions, both are AMRAAM-capable.