The United States Air Force has retired its final McDonnell Douglas KC-10 Extender tanker and cargo aircraft. The KC-10 Extender is a military version of the iconic three-engine McDonnell Douglas DC-10 airliner and was developed to supplement the numerous KC-135 Stratotankers. The KC-10 Extender has now completed its 42 years of service and is heading for retirement at the famous boneyard at Davis-Monthan Air Force Base.