Hawker Siddeley Harrier AV-8As to the AV-8C configuration—the work focused mainly on extending useful service lives and improving VTOL performance. The AV-8C and the remaining AV-8A Harriers were retired by 1987. These were replaced by the Harrier II, designated as the AV-8B, which was introduced into service in 1985. The performance of the Harrier in USMC service led to calls for the United States Air Force to procure Harrier IIs in addition to the USMC's own plans, but these never resulted in Air Force orders. Since the late 1990s, the AV-8B has been slated to be replaced by the F-35B variant of the
Hawker Siddeley Harrier the integration of American radios and Identification Friend or Foe (IFF) systems; furthermore the outer pylons, unlike the RAF aircraft, were designed from delivery to be equipped with self-defence AIM-9 Sidewinder heat-seeking air-to-air missiles. Most of the AV-8As had been delivered with the more powerful Pegasus engine used in the GR.3 instead of the one used in the earlier GR.1. Two-seat Harriers were operated for training purposes; the body was stretched and a taller tail fin added. The RAF trained in the T.2 and T.4 versions, while T.4N and T.8 were training versions the Navy's Sea Harrier, with appropriate fittings.