The Boeing KC-135 Stratotanker is a military aerial refueling aircraft. It and the Boeing 707 airliner were developed from the Boeing 367-80 prototype. The KC-135 was the US Air Force’s first jet-powered refueling tanker and replaced the KC-97 Stratofreighter. The KC-135 was initially tasked to refuel strategic bombers, but was used extensively in the Vietnam War and later conflicts such as Operation Desert Storm to extend the range and endurance of US tactical fighters and bombers.The KC-135 entered service with the United States Air Force (USAF) in 1957; it is one of six military fixed-wing aircraft with over 50 years of continuous service with its original operator. The KC-135 is supplemented by the larger KC-10. Despite increased maintenance costs, studies conclude many of the aircraft could be flown until 2040. The aircraft will eventually be replaced by the Boeing KC-46 Pegasus.