The aircraft is primarily employed on light attack or multi-role missions, ranging from close air support of ground troops to armed reconnaissance.

While retaining the general layout of its predecessor, the aircraft incorporates a new, larger composite wing with an additional hardpoint on each side, an elevated cockpit, a redesigned fuselage and other structural and aerodynamic refinements.

In short takeoff and landing configuration, the AV-8A (American designation for the Harrier) carried less than half of the smaller A-4 Skyhawk's payload (4,000 lb (1,800 kg), over a more limited radius.

Hawker Siddeley focused on a new larger wing that could be retrofitted to existing operational aircraft, while McDonnell Douglas independently pursued a less ambitious, though still expensive, project catering to the needs of the U.S. military.

[14][15] The United States Navy (USN), which had traditionally procured military aircraft for the USMC, insisted that the new design be verified with flight testing.

[7] The British government was enticed by the lower cost of acquiring Harriers promised by a large production run, and the fact that the U.S. was shouldering the expense of development.

[28] The second and third FSD aircraft, which introduced wing leading-edge root extensions and revised engine intakes, first flew in April the following year; the fourth followed in January 1984.

[33] With export interest from Brazil, Japan, and Italy serving as a source of encouragement to continue development of the Harrier II, McDonnell Douglas commenced work on a night-attack variant in 1985.

[37][38] In June 1987, as a private venture, BAe, McDonnell Douglas, and Smiths Industries agreed on the development of what was to become the AV-8B Plus with the addition of radar and increased missile compatibility.

[41][N 3] Spain also participated in the program, the delivery of its last refurbished aircraft occurring in December 2003, which marked the end of the AV-8B's production; the final new AV-8B had been delivered in 1997.

[65][66] These hardpoints give it the ability to carry a total of 9,200 lb (4,200 kg) of weapons, including air-to-air, air-to-surface, and anti-ship missiles, as well as unguided and guided bombs.

On the underside of the fuselage, McDonnell Douglas added lift-improvement devices, which capture the reflected engine exhaust when close to the ground, giving the equivalent of up to 1,200 lb (544 kg) of extra lift.

The supercritical wing, hands-on-throttle-and-stick (HOTAS) control principle, and increased engineered lateral stability make the aircraft fundamentally easier to fly.

Using the leading edge root extensions, the wing allows for a 6,700 lb (3,035 kg) increase in payload compared with the first-generation Harriers after a 1,000 ft (300 m) takeoff roll.

[78] The Harrier II was the first combat aircraft to extensively employ carbon-fiber composite materials, exploiting their light weight and high strength;[80][81] they are used in the wings, rudder, flaps, nose, forward fuselage, and tail.

It differed from the original aircraft in having a forward-looking infrared (FLIR) camera added to the top of the nose cone, a wide Smiths Industries head-up display (HUD), provisions for night vision goggles, and a Honeywell digital moving map system.

[86][87] The Harrier II Plus is very similar to the Night Attack variant, with the addition of an APG-65 multi-mode pulse-Doppler radar in an extended nose, allowing it to launch advanced beyond-visual-range missiles such as the AIM-120 AMRAAM.

According to aviation author Lon Nordeen, the changes "had a slight increase in drag and a bit of additional weight, but there really was not much difference in performance between the [–408-powered] Night Attack and radar Harrier II Plus aircraft".

In the operational evaluation (OPEVAL), lasting from 31 August 1984 to 30 March 1985, four pilots and a group of maintenance and support personnel tested the aircraft under combat conditions.

The aircraft was graded for its ability to meet its mission requirements for navigating, acquiring targets, delivering weapons, and evading and surviving enemy actions, all at the specified range and payload limits.

[89] The second phase of OPEVAL, which took place at MCAS Yuma from 25 February to 8 March, required the AV-8B to perform fighter escort, combat air patrol, and deck-launched intercept missions.

[102] In a single sortie from USS Bonhomme Richard, a wave of Harriers inflicted heavy damage on a Republican Guard tank battalion in advance of a major ground assault on Al Kut.

Despite the Harrier's high marks, the limited amount of time that each aircraft could remain on station, around 15–20 minutes, led to some calls from within the USMC for the procurement of AC-130 gunships, which could loiter for six hours and had a heavier close air support capability than the AV-8B.

[108] In addition to major conflicts, USMC AV-8Bs have been deployed in support of contingency and humanitarian operations, providing fixed-wing air cover and armed reconnaissance.

[123] On 1 August 2016, USMC Harriers from USS Wasp began strikes against ISIL in Libya as part of manned and unmanned airstrikes on targets near Sirte, launching at least five times within two days.

[124] In January 2024 during the Red Sea crisis one of the Harriers was modified for air defense; its pilot Captain Earl Ehrhart is reported to have shot down seven Houthi suicide attack drones.

[131] The Harriers, flown by five Italian pilots, accumulated more than 100 flight hours and achieved 100% availability during the three-month deployment, performing reconnaissance and other missions.

[145] Following the decommissioning of Príncipe de Asturias in February 2013,[146] the sole naval platform from which Spanish Harrier IIs can operate is the amphibious assault ship Juan Carlos I.

[165] Author Lon Nordeen notes that several other USMC single-engine strike aircraft, like the A-4 Skyhawk and A-7 Corsair II, had higher accident rates.

Cutbacks in senior maintenance personnel and pilot mistakes had a disastrous effect on the safety of the American-operated AV-8B and unfairly gained it a negative reputation in the U.S.