The KC-135 was originally tasked with supporting Strategic Air Command bombers; however, it became necessary during the Vietnam War for it to extending the range and combat time of the F-104 and F-4 fighter-bombers. It was used extensively in the Vietnam War, Operation Desert Storm, Operation Iraqi Freedom, and is currently being utilized for support in Operation Enduring Freedom. Currently, 481 KC-135's are managed by the Air Mobility Command, 292 are operated by Air force Reserve and Air National Guard units. Though plans to replace the KC-135 with the KC-46, studies have shown that the KC-135 could be flown until 2040.
With four turbofan engines mounted underneath it's 35-degree swept wings, the KC-135 boasts a max takeoff weight of up to 322,500lbs (146,300kg). A single boom mounted on the rear of the aircraft, allows it to transfer nearly all of its internal fuel for routine refuels or even consolidation with other KC-135's. On average, each KC-135 logs between 710 and 800 hours annually, double the amount planned, in order to meet air born refueling requirements.