McDonnell Douglas AV-16 Advanced Harrier Article

An advanced Harrier proposal from 1973. The Advanced Harrier project gained the unofficial designation of AV-16 while Hawker Siddeley assigned the designation of P.1184 to it.

From Wikipedia: “In December 1973, a joint American and British team completed a project document defining an Advanced Harrier powered by the Pegasus 15 engine. The Advanced Harrier was intended to replace the original RAF and USMC Harriers, as well as the USMC's A-4. The aim of the Advanced Harrier was to double the AV-8's payload and range, and was therefore unofficially named AV-16. The British government pulled out of the project in March 1975 owing to decreased defense funding, rising costs, and the RAF's insufficient 60-aircraft requirement.[9][11][12] With development costs estimated to be around £180–200 million (1974 British pounds), the United States was unwilling to fund development by itself, and ended the project later that year.”

See article here

A very good Harrier development article is here