In August 1954 the USAF chose a derivative of the model 387-80 prototype as replacement for its Boeing KC-97 tanker. The first KC-135 flew in August 1956, and deliveries of 732 aircraft began in June 1957. The KC-135 has a narrower fuselage than the model 707 airliner derived from the same prototype, and a different interior including the tanks that feed the Boeing "flying boom" refueling systems. Four turbojets, mounted under wings swept 35 degrees, power the KC-135. Nearly all internal fuel can be pumped through the tanker's flying boom, the KC-135's primary fuel transfer method. A special shuttlecock-shaped drogue, attached to and trailed behind the flying boom, is used to refuel aircraft fitted with probes. An operator stationed in the rear of the plane controls the boom. A cargo deck above the refueling system holds passengers or cargo. Depending on fuel storage configuration, the KC-135 can carry up to 83,000 pounds (37,350 kilograms) of cargo. The KC-135 tanker fleet made an invaluable contribution to the success of Operation Desert Storm in the Persian Gulf, flying around-the-clock missions to maintain operability of allied warplanes. The KC-135s form the backbone of the Air Force tanker fleet, meeting the aerial refueling requirements of bomber, fighter, cargo and reconnaissance forces, as well as the needs of the Navy, Marines and allied nations.