Pentagon officials have indicated that September will be the most likely date to issue a draft request for proposals to replace the air force’s aging aerial tanker fleet.

The US Air Force presently has a fleet of 415 KC-135 refuelling aircraft most of which have been in service for about 50 years.

Last year, the Defense Department cancelled a $35bn, 179-plane contract awarded to Northrop Grumman and European partner EADS after government auditors upheld a challenge from Boeing, which lost out on the bid.