Douglas remained lukewarm about the jet airliner project but believed that the Air Force tanker contract would go to two companies for two different aircraft, as several USAF transport contracts in the past had done. In May 1954, the USAF circulated its requirement for 800 jet tankers to Boeing, Douglas, Convair, Fairchild, Lockheed, and Martin. Boeing was just two months away from having its prototype in the air. Just four months after issuing the tanker requirement, the USAF ordered the first 29 KC-135s from Boeing. Besides Boeing's ability to provide a jet tanker promptly, the flying-boom air-to-air refueling system was also a Boeing product from the KC-97.