Tal como comenta Alex, el P.1127, el prototipo del que derivó el Hawker Siddeley Harrier y los AV-8A, ya estaba volando en 1960, e hizo sus pruebas en el portaviones HMS Ark Royal en 1963 y 1969 con un Harrier GR.1 a bordo del HMS Blake. Los americanos ya operaban escuadrones de harriers de los marines en 1971, el USS Guam empezó las pruebas del los AV-8A en 1972, un año antes del dedalo.
The Marine Corps accepted its first AV-8A on January 6, 1971 at the Dunsfold Aerodrome, England and began testing it as NAS Pax River on January 26. The AV-8A entered service with the Marine Corps in 1971, replacing other aircraft in the Marines' attack squadrons. The service became interested in performing ship-borne operations with the Harrier. Admiral Elmo Zumwalt promoted the concept of a Sea Control Ship, a 15,000-ton light carrier equipped with Harriers and helicopters, to supplement the larger aircraft carriers of the US Navy. An amphibious assault ship, USS Guam, was converted into the Interim Sea Control Ship and operated as such between 1971 and 1973 with the purpose of studying the limits and possible obstacles for operating such a vessel. Since then the Sea Control Ship concept has been subject to periodic re-examinations and studies, often in the light of budget cuts and questions over the use of supercarriers.[N 12]
In the summer of 1971, Guam was chosen as a test vessel for Admiral Elmo Zumwalt's Sea Control Ship concept. This ship was to operate a few VSTOL fighters and some ASW helicopters in order to free up supercarriers from convoy duty during a conflict with the Soviet Union. On 18 January 1972, she began extensive testing and in 1974 deployed in the Atlantic as a sea control ship with Marine Corps AV-8A Harrier VSTOL fighters and Sea King ASW helicopters. Guam completed the SCS tests and reassumed her role as an Amphibious Assault Ship on 1 July 1974. In October 1974 her aircraft complement, operated by the US Marine Corps, comprised six AV-8A, eight CH-46F Sea Knights, five CH-53D Sea Stallions and two Bell UH-1N Iroquis utility helicopters.