The KC-10 was the first produced and served as the demonstrator for the series. Early in the 1970s, it became evident that the KC-135 Stratotanker had limited operational capabilities and could not meet the demands of the U.S. Air Force. To augment those duties and obtain a larger, long-range, general-purpose tanker, the KC-10 Extender was purchased in 1978 and entered service in 1981. Although it retained 88% commonality with the DC-10, it included additional systems and equipment needed for its Air Force mission, including military-grade avionics, an aerial refueling boom and hose-and-drogue system, a seated refueling operator station, a refueling receptacle, and satellite communications. The KC-10 was crucial in supporting global military operations by allowing strategic aircraft to reach their destinations without stopping, providing tactical fighters with simultaneous in-flight refueling and cargo airlift during long-range deployment, and reconfiguring when needed into an aeromedevac role to transport litter patients.