Because of the special fuel requirements of the SR-71, the KC-135Q-model was designed to isolate two separate fuel types within its fuel cells. This design gave the KC-135Q the distinction of being the only airplane capable of refueling the fastest airplane in the world. All KC-135Qs are modified from the original version, the KC-135A. The modification program started in 1966 and by 1968 a total of 56 jets made the transformation.
After two fuel shortages through the 1970s and '80s, a decreasing force and an ever-increasing threat abroad, the demand for tanker support increased, officials noted. To meet this demand, changes in the KC-135 were necessary to do more with less. The answer was to upgrade the 1950s technology engines that were originally designed and built into the KC-135A. These engines, the J-57, lacked the power and fuel efficiency needed in modern wartime environment.
In 1984 the first upgrade jet, the KC-135R, was accepted into the Air Force inventory. With its CFM-56 engines, it could produce over 22,000 pounds of thrust compared to the J-57s 13,500 pounds. In addition, the KC-135R was 30 percent more fuel efficient than the KC-135A or Q. These changes meant the capability of carrying a much larger payload with much greater cost efficiency. The result was evidenced by the huge success of the air campaign over Iraq.
The KC-135T version of the KC-135 met the ever-increasing demand for more efficient and reliable air refuelers, yet still retains its capability to refuel the SR-71. Aircraft 58-0099, the last KC-135Q model in the Air Force, departed Fairchild AFB on 29 September 1995. Along with this departure went the characteristic billowing black smoke and thunderous sound that accompanies every Q-model takeoff. When it returned, it wore the designation of a KC-135T.
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