The Boeing KC-135 Stratotanker was the first jet powered aerial refueling tanker of the US Air Force, replacing the KC-97 Stratotanker. Similar in design to the later and enlarged Boeing 707 airliner, it was initially tasked to refuel strategic bombers, but was used extensively in the Vietnam war and later conflicts such as Desert Storm to extend the range and endurance of both Air Force and Navy tactical fighters and bombers.
Serving with the United States Air Force since 1957, it is one of just six military aircraft with over 50 years of continuous service with the original service along with the Tupolev Tu-95, the C-130 Hercules, the B-52 Stratofortress, the English Electric Canberra and the Lockheed U-2. Supplemented by the larger KC-10, complete replacement is still under study by the Air Force. Despite increased maintenance costs, studies conclude many of the aircraft could be flown until 2040, with ages reaching 80 years before reaching lifetime flying hour limits.