However, I do think the KC-135 fleet will soon heading for its sunset years as the KC-46 replaces them. The initial order for 100 planes could be expanded to possibly another 150 to 200 planes, which will allow the complete phase out of the KC-135 fleet.
>> The KC-135 is still viable because the USAF was able to use a large number of parts salvaged from scrapped Boeing 707 airliners ...
Roger that. I was furloughed from United from ‘81 to late ‘84, lived in Miami, and spent time ferrying 707s out to the boneyard. The AF stripped off the JT3D-3B engines and the horizontal tail feathers.
The original tanker J-57 engines did not have reversers and drove the brake temps through the roof when stopping. Tanker drivers must have been in heaven the first time they pulled the reversers!
A design defect in the 707/-135s was that when the aircraft made approaches and landings with flaps in the 40 position, it created a low period (1-2 second) pitch oscillation that ultimately overstressed the horizontal tail. After one snapped off in Mozambique, most airlines (and I think the AF) restricted landings to 30 flaps.
An interesting note from AF flight school days (Vance 70-02): If you had plans to go to the airlines after your AF hitch was up, two airplanes were high on your list - C-141s and tanks. 141 drivers went to MAC and got lots of cross country hours BUT only for a year. Then, you got sent to Viet Nam in a light aircraft (Gooney bird, Cessna MixMaster, C-123, etc.).
I chose the 135, but it came with another horror: SAC. “SAC sucks” was the expression, along with “A suck for SAC is a blow for freedom”. By the time I got there in 1970, things had changed. Lots of TDY and fighter drags across the pacific. Not much alert duty.
Ended up as an IP (instructor pilot); got out after 5-1/2 years with 2,000 hours total time; the minimum for the airlines.
This is/was true only for selected components like the JT3-Ds (KC-135E) and the taller tail cap.
It is a common myth that the KC-135 is a modified B707. In fact, the reverse is more true. The KC-135 design was actually finalized before the B707's. The 707 profited significantly from the KC-135 design.
The KC-135 has a forward crew access hatch, smaller fuselage diameter and laminated wood decking in addition to accomodations for the fuel bladders. Anyone who has laced those in will appreciate the fuselage diameter difference. The wings, wingroots and flaps have significant geometric differences too between the 135 and 707.
Some commercial 707s have been modified as tankers for the some clients and some commercial operators.