The KC-135Q Story, Part One: Tweaking the Stratotanker to Refuel a Mach 3+ Spy Plane

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The KC-135Q Story, Part One: Tweaking the Stratotanker to refuel a Mach 3+ Spy Plane

Why the series suffix ‘Q’ was selected is unknown. Using normal designation procedures, the KC-135Q should have been called the KC-135C as the MDS ‘KC-135B’ had already been allocated to the airborne command post then under development.

The KC-135Q Story, Part One.

On Jul. 4, 1956, Central Intelligence Agency (CIA) pilot Hervey Stockman took off in Article 347 from Wiesbaden AB in West Germany on Mission #2013. His U-2 climbed to 70,000ft (21,336m) before turning east to overfly East Germany, Poland, Minsk, Leningrad, Estonia, Latvia, and back over Poland. Stockman landed after eight hours and 45 minutes, bringing the first U-2 overflight of the Soviet Union to a successful end. Much to the surprise of CIA planners and Lockheed designers, however, Soviet radar tracked Stockman’s U-2 the entire time it was over Soviet territory. The U-2’s absolute advantage in altitude had meant that it remained beyond the reach of Soviet interceptors, but US officials were concerned that high-flying MiGs and nascent surface-to-air missiles (SAM) would eventually render this moot. Indeed, on  Oct. 7, 1959, a Red Chinese SA-2 Guideline SAM (bought from the USSR) claimed the first SAM kill when it shot down Republic of China Air Force (RoCAF) RB-57D 53-3978. Although the RB-57D flew some 10,000ft (3,048m) lower than the U-2, it was just a matter of time before a lucky shot would claim a U-2. After 23 unsuccessful attempts and seven months after the RoCAF RB-57D loss, a Soviet SA-2 finally managed to shoot down a CIA U-2 on May 1, 1960 during a deep overflight of the USSR.

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As explained by Robert S Hopkins III in his book The Boeing KC-135 Stratotanker, aside from the political fallout of the `U-2 Incident,’ plans were already underway to replace the U-2 with a more capable platform for future overflights. As part of project GUSTO, the CIA had previously accepted Clarence ‘Kelly’ Johnson’s 1958 ‘Archangel’ design for a new strategic reconnaissance airplane. The newest product of Lockheed’s ‘Skunk Works’ — the OXCART A-12 — would fly in excess of three times the speed of sound and at altitudes above 80,000ft (24,384m), far beyond the reach of the SAMs that claimed Frank Powers’ U-2. The A-12 was originally intended to operate unrefueled but the installation of additional sensors increased its gross weight and reduced its available fuel capacity, limiting it to less than an hour of useful flight time. The solution to this shortcoming lay in aerial refueling, but selecting the KC-135 was not without significant challenges. The A-12’s PF-1 fuel was extremely caustic and eroded existing fuel bladders and fuel lines. Any tanker that would carry PF-1 required special fuel tanks and lines separate from those needed to haul the tanker’s own regular JP-4 jet fuel. To accommodate the A-12’s special fuel, the liners in the KC-135’s forward body, center wing, aft body, and upper deck fuel tanks, along with the air refueling manifold would need to be replaced with a special ceramic material impervious to PF-1, adding considerable weight (and cost) to the airplane. The actual rendezvous and refueling procedures would also differ dramatically for the Mach 3+ A-12, requiring additional navigation and communication equipment. During 1961-62 the CIA funded the modification of the initial cadre of KC-135s (determined by the minimum number needed to sustain maximum flight operations for 10 A-12s). SAC identified 21 KC-135As for modification, all low-time airframes with good maintenance records.

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The first A-12 air refueling took place on Jul. 11, 1962 during the 24th flight of Article 121 (60-0924). A-12s were still equipped with two Pratt & Whitney J75 engines (pending delivery of the production Pratt & Whitney J58s) so air refueling tests used JP-4. Crew for this first refueling was from the 924th AREFS, 93rd BW at Castle AFB. Originally the A-12 refueling mission was to be assigned the 924th AREFS which was closer to the desert home of the A-12s at Groom Lake, NV. The subsequent development of the SENIOR CROWN SR-71 altered this plan. Since the SR-71 would be an Air Force asset (versus the A-12 which was a CIA asset), SAC argued that the SR-71s and their dedicated KC-135s should be co-located at Beale AFB, CA, so the refueling mission went to the 903rd AREFS, 4126th SAW rather than the 924th AREFS. SAC SR-71 operations were known as GIANT ELK. Combat reconnaissance missions over Southeast Asia and North Korea beginning in 1968 were known as GIANT SCALE, and the program name for KC-135 refueling support for operational reconnaissance missions was GIANT BEAR.

In an effort to eliminate the caustic PF-1 fuel for the A-12, Shell Oil Company, Ashland Oil Company, and Monsanto Chemical Company developed JP-7, a hydrocarbon fuel of low vapor pressure for the SR-71 and the YF-12 interceptor. The eventual use of JP-7 eliminated the need for the expensive and heavy ceramic linings, which were removed and replaced by the standard rubber liners. The KC-135 tankers could burn JP-7, although not as a primary fuel (much as B-47s could burn AvGas from KC-97s). Following an ‘air flush’ of the JP-7, the KC-135 could then carry JP-4 in all of its tanks, as well as offload it to any receiver.

Throughout the first four years of operations, A-12 and SR-71 tankers were designated simply as KC-135As. On  Jun. 16, 1966 Aeronautical Systems Division (ASD) specified the redesignation en masse of the dedicated KC-135As as KC-135Qs, although the actual MDS change did not take place until the latter half of 1967, and then in several tranches. Why the series suffix ‘Q’ was selected is unknown. Using normal designation procedures, the KC-135Q should have been called the KC-135C as the MDS ‘KC-135B’ had already been allocated to the airborne command post then under development.

The KC-135Q Story, Part One: Tweaking the Stratotanker to Refuel a Mach 3+ Spy Plane

Given the extremely secretive development of the A-12, this out-of-sequence designation might best be explained by security concerns, or perhaps the motivation for this unusual designation was recorded but not forwarded to the ASD history office. Still, official Air Force documents record no ‘special reason for giving it the Q designation.’

By the end of 1966 21 KC-135Qs had been modified and were in service with the 903rd AREFS — by now part of the 456th SAW — at Beale AFB. In addition to their support of SR-71 and A-12 operations, KC-135Qs and their crews shared operational commitments with B-52Gs assigned to the 744th BS, also stationed at Beale AFB. As the demands on the KC-135Qs grew, it became clear that the fleet would have to grow to accommodate these increasing requirements due to the need for a large number of ready-to-go spare aircraft. Since A-12 and SR-71 missions were critically dependent upon receipt of their scheduled fuel at each refueling point, a ground or air abort by a KC-135Q effectively scrubbed the entire reconnaissance mission. This was especially frustrating if the affected tanker was scheduled for the initial air refueling. Standard procedures called for the SR-71 to take off with 55 to 60% full fuel load to ensure that the pilot could maintain lateral maximum control in the event of an engine failure on takeoff, with the first air refueling scheduled some 15-20 minutes after takeoff. This also filled the tanks to allow purging of air by nitrogen gas as they emptied during the course of the flight to prevent cavitation or other problems. As each A-12 and SR-71 mission cost several hundred thousand dollars, it was absurd to cancel it because of a problem with a single tanker. Consequently, both air and ground spares were required for many operational sorties. The A-12s and SR-71s had to get their fuel, regardless of how many tankers were needed to get it there.

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In 1967 OCAMA converted 35 additional airplanes into KC-135Qs, with 20 KC-135As from the 70th AREFS, 43rd BW at Little Rock AFB, AR, and 15 from the 306th AREFS, 306th BW at McCoy AFB, FL. Because of the expense involved, SAC elected not to convert these airplanes into ‘full’ KC-135Qs, and they were known informally as ‘partial Qs’. They lacked a full avionics suite —especially the AN/ARN-90 TACAN and the LORAN A — although the intention was that it could be installed with sufficient notice prior to a mission. Realistically, however this proved difficult to undertake, if ever. Of the 56 KC-135Q conversions, 21 were full modifications based at Beale AFB and 35 were partial Qs at McCoy AFB and Little Rock AFB.

The KC-135Q Story, Part One: Tweaking the Stratotanker to refuel a Mach 3+ Spy Plane

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Photo credit: U.S. Air Force

1 COMMENT

  1. Once, while TDY from Carswell Texas to Mildenhall Air Base England, in 1978, we had to support the ferry of an SR-71 out of England. I was crewing a KC-135A. We had to de-fuel and purge the JP4 from our center, forward and aft body tanks and load JP7 to refuel the SR-71. We then returned to Mildenhall and purged those tanks so we could put JP4 back into the tanks. It’s was called flying “ dirty”. The KC-135 tankers could burn JP-7, although not as a primary fuel, and only under emergency situations.
    Here’s a picture I took of one of our refuels. Once, while TDY from Carswell Texas to Mildenhall Air Base England, in 1978, we had to support the ferry of an SR-71 out of England. I was crewing a KC-135A. We had to de-fuel and purge the JP4 from our center, forward and aft body tanks and load JP7 to refuel the SR-71. We then returned to Mildenhall and purged those tanks so we could put JP4 back into the tanks. It’s was called flying “ dirty”. The KC-135 tankers could burn JP-7, although not as a primary fuel, and only under emergency situations.
    Here’s a picture I took of one of our refuels. Once, while TDY from Carswell Texas to Mildenhall Air Base England, in 1978, we had to support the ferry of an SR-71 out of England. I was crewing a KC-135A. We had to de-fuel and purge the JP4 from our center, forward and aft body tanks and load JP7 to refuel the SR-71. We then returned to Mildenhall and purged those tanks so we could put JP4 back into the tanks. It’s was called flying “ dirty”. The KC-135 tankers could burn JP-7, although not as a primary fuel, and only under emergency situations.

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