Without doubt, the KC-135 will go down in aviation history as the Gooney Bird of the jet era. They have been flying since 1957 and are still in service today. There has been evolution in engines but the basic airframe is mostly unchanged. From the Air Force Link....
Of the original KC-135A's, more than 415 have been modified with new CFM-56 engines produced by CFM-International. The re-engined tanker, designated either the KC-135R or KC-135T, can offload 50 percent more fuel, is 25 percent more fuel efficient, costs 25 percent less to operate and is 96 percent quieter than the KC-135A.
My connection goes back to the A model or "water wagon" as we called them. The original engines were P&W JT3's before the by pass fan was invented. This engine was augmented with water injection on take off for cooling and more power. No, the water did not provide more thrust, but the cooling it offered permitted more fuel burn and more thrust. As I recall, the electric water pumps injected about 3000 pounds (600 gallons) of water over a 90 second period. The navigator timed the water run so we had an idea when it would quit because the loss of thrust was quick and on a hot day was quite dramatic. The reason the new engines are 96% quieter is because those JT3's were the about the nosiest engines ever with H2O injection. People living near an AF base could hear them for miles.
Just a few quick notes on this remarkable airplane and its early JT3's. The empty weight of the A model was right at 100,000 pounds. We flew them grossed out at over 300,000 pounds for some missions during the Viet Nam fiasco. During one period we as crew members were aloft 90 hours a month but the airplanes flew day and night probably four times that amount, they were very reliable. An engine failure was extremely rare. We used to haul F-105 fighter pilots out of the war zone on the jump seat when they went on R&R. It was interesting how they would sit up and try to figure out if we were going to fly (or not) roaring down a 12000' runway for about 11,000'.
Later at TWA it was the 707 with the fan engines, wow, what a queen of the fleet if ever there was one. When these machines were retired, one had 36000 hours TT and 2 of the JT3's were the original engines from the factory. Many of the TWA engines went to USAF 135's to replace the water wagons. I think the CFM's came later and probably replaced the fan JT3's.
Enough rambling on this great airplane...for sure Bruce will give you a great tour. Another tour of this great machine - Air Force 1, the original - can be had at the Pres. Reagan Memorial Library at Simi Valley, California.