The Boeing KC-135 Stratotanker is the predominant variant of the C-135 Stratolifter family of transport aircraft. The KC-135 was the US Air Force's first jet-powered refueling tanker and replaced the Boeing KC-97 Stratofreighter, the military derivative of the Stratocruiser piston airliner.
The KC-135 was initially tasked with refuelling 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.
An RC-135S of the US Air Force
A total of 820 C/KC-135s were built in Renton, Washington: 732 as aerial tankers and 88 modified for special purposes. While the US Air Force was the major operator, the aircraft has also served with the air forces of France, Turkey, Singapore and the UK.
Special variants were developed for reconnaissance and command post roles, including the RC-135V/W Rivet Joint, RC-135U Combat Sent, RC-135S Cobra Ball, WC-135 Constant Phoenix (AKA “The Nuke Sniffer”), E-3 Sentry and EC-135 Looking Glass aircraft were operated by Strategic Air Command from 1963 through 1992, when they were reassigned to the Air Combat Command.
Initially powered by Pratt & Whitney J-57 turbojets, the C-135 family has been continuously adapted and modified to extend its service capabilities, including re-skinning the wings with an improved aluminium alloy and installing more powerful and fuel-efficient engines. Early upgrades saw the J-57s replaced by P&W TF33 turbofans and later a major re-engining programme involved the installation of CFM International CFM56s. Two CFM56-powered KC-135Rs could do the work of three KC-135As.
In February 2011, Boeing was contracted to build the USAF's next-generation tanker aircraft derived from the 767. Dubbed the KC-46, the new tanker will replace around half of the USAF's 400 KC-135 tankers.