Boeing's 367-80 prototype jet transport, first introduced in May 1954, became the basis for the KC-135. On September 1, 1954, Strategic Air Command ordered the first 29 of its future 732-plane fleet, almost one KC-135 for each B-52 bomber. First accepted in 1957, the last KC-135 was delivered in 1965. Starting in 1981, approximately 157 Air Force Reserve and Air National Guard KC-135A models had their J-57 water-injected turbojet engines replaced with refurbished TF-33 engines. Redesignated as the KC-135E, the 14% more fuel efficient engines allowed the offload of more fuel, and the thrust reversers shortened required landing rollout. About the same time, a different upgrade program replaced the engines on approximately 415 KC-135-A models with new CFM-56 turbofan engines, a modification that increased fuel efficiency by 25% while reducing noise by 96%. First flown in 1982, the newly designated KC-135R was accepted into the Air Force inventory in 1984. In addition to air refueling, aeromedical evacuation, and traditional airlift, some thirty specialized variants flew missions ranging from flying command post, to reconnaissance and signal intelligence gathering, to zero gravity training for NASA. This KC-135E aircraft was acquired February 27, 1958, and was the 50th aircraft built. It was converted into an "E" model in 1984 and served in Canada, Philippines, Spain, Taiwan, Thailand, and various US bases. It is painted in the Air Mobility Command "Proud Gray" color scheme it used from August 2004 until March 2009, while assigned to the 126th air refueling wing, Illinois Air National Guard. It honors all those who have flown and supported the KC-135 Stratotanker mission over the past 50 years and those who will continue to do so into the future.