The RC-135 was based on the transport aircraft Boeing C-135 and was first flown on 28th April 1956. The main differences in comparison to the RC-135 are lots of new systems in it, like Electronic Intelligence (ELINT) and Communications Intelligence (COMINT) systems. Some versions are known for their enlarged, so called, “hog nose” radome, and for their aerodynamic coverings at the forward fuselage, in which enhanced radar systems are stored.
Out of the RC-135A, all variants are able to perform air-to-air refuelling. Since the end of the 1990s, some RC-135s were equipped with new and more powerful CFM International F108 turbofan engines.
At the beginning of the 1960s, the Strategic Air Command (SAC) of the US Air Force received the first RC-135 aircraft. Some of them were used to replace old bombers, which were modified for reconnaissance roles. Only the RC-135A and the RC-135B were built by Boeing newly, while the other variants were upgraded C-135s, KC-135s and RC-135s. Some aircraft were unique, but all of them were equipped with highly advanced technology. Four RC-135s were lost, one RC-135E, two RC-135S and –T, during these accidents, 28 people died.
As of 2007 only 22 RC-135 of the variants -S, -U, -V and –W were in service with the USAF. They are stationed at the 55th Strategical Reconnaissance squadron of the Air Combat Command and are based at the Offutt Air Force Base in Nebraska. By 2014, the Royal Air Force wants to buy four RC-135Ws, to replace their Nimrod R1 aircraft.