The new KC-X refuelling tanker is set for its first flight test in 2012 with a view to undertaking its first missions in 2017, according to the US Air Force.
The USAF submitted the request for proposals (RFP) in late February, according to Defense News.
Initially, the air force will buy four KC-X test aircraft, to use them for test flights and later the aircraft will be modified into a production aircraft.
According to the Pentagon's plans the first of seven new tankers will be produced by 2013, and delivered to the air force in 2015.
The current RPF requires 18 aircraft to be delivered by 2017.
Under the KC-X tanker programme, worth $40bn, the USAF will acquire next-generation 179 tankers, to replace its aging KC-135 Stratotankers.
