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
Harrier Jump Jet of the upgraded "Sea Harrier FA2"; this version entered operational service on 2 April 1993. The Sea Harrier was also procured by the Indian Navy, the first Indian Sea Harriers were entered squadron service during December 1983. 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. Early efforts concentrated on the development of an improved Pegasus engine, designated the "Pegasus 15", which was being tested by Bristol Siddeley. During August 1981, the program received a boost when British Aerospace (BAe) and McDonnell Douglas signed