The Aircraft
The KC-135 was the US Air Force’s first jet refueling aircraft, replacing the KC-97. The 135 was developed from the same prototype as the 707, but has much more in common with the Model 720. The 135 entered service with the USAF in 1957. The last KC-135 was delivered in 1965.
The KC-135E was an interim between the KC-135A and R. The E model came about when it became apparent that the A model just didn’t have the power and range needed to support the global mission of the US Air Force. The fix is the same one used on the Boeing 707 and 720, updating the engines from P&W J-57s to TF-33s. The re-engining continued with the KC-135R, which has GE/SNECMA CFM-56 engines. The Air National Guard and Air Force Reserve flew the E model.