The SR-71 Spy Plane Was a Legend. Refueling It Was Just as Legendary.

an AN/ARC-50 known as ‘Comm 3’ — also provided distance measurement between the KC-135Q and A-12/ SR-71.

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How was it done? 

by Dario Leone

The major differences between the KC-135Q and other KC-135s were primarily related to the fuel system and rendezvous and communications equipment. The KC-135Q utilized two single-point ground refueling receptacles — one in each main landing gear wheel well. Other KC-135s have only one located in the right main gear well. On the KC-135Q, the left system services the airplane’s JP-4 in the wing tanks and the right system fills the JP-7 normally carried in the body fuel tanks (the forward body, center wing, and aft body tanks plus the upper deck tank). The KC-135Q could simultaneously carry a maximum of 74,490 lb (33,788kg) of JP-7 and 110,000 lb (49,896kg) of JP-4. To account for changes in the airplane’s center-of-gravity (cg) during SR-71 refueling operations, 850 lb (385kg) of ballast was added to the lower nose compartment.

As explained by Robert S Hopkins III in his book The Boeing KC-135 Stratotanker, rendezvous and communications equipment differences in a ‘full Q’ included the addition of a third UHF radio and an AN/ARN-90 TACAN, both located at the navigator’s station. The third UHF radio — an AN/ARC-50 known as ‘Comm 3’ — also provided distance measurement between the KC-135Q and A-12/ SR-71. In the partial Q, Comm 3 was the sole source of air-to-air distance measurement for the rendezvous with an A-12 or SR-71. The power of the Comm 3 was considerable, with two KC-135Qs reported to have maintained ranging out to a distance of 700 miles (1,126km). The TACAN provided the SR-71 with range and bearing data for a head-on rendezvous, but in early use was notoriously unreliable in the air-to-air mode. KC-135Qs were at one time equipped with LORAN-A for precise maintenance of their orbit at air refueling control points (ARCPs) beyond the range of existing navigational aids such as TACANs. This equipment was eventually removed. In the late 1980s a satellite communications (SATCOM) antenna was installed on the upper forward fuselage. Strobe lights were installed on the upper and lower fuselage and tail, although similar strobes mounted on the wingtips were deactivated after several wing fires and explosions were attributed to them. On some KC-135Qs the boom operator had a boom interphone system installed which allowed radio silent communication with the receiver once boom contact is made. A searchlight was mounted in bottom of the tail cone of the KC-135Q to illuminate the air refueling envelope. This feature was installed as part of the KC-135Q modification and was different from the tail-mounted floodlight (TMF) later installed on all KC-135s and KC-135Qs. All KC-135Qs had high-speed air refueling booms.

Refueling operations with the A-12 and SR-71 were unique and demanding. As the receivers were on classified reconnaissance missions, operational and communications security were much more stringent than in routine tanker operations. The dependency of the receiver on the tanker, especially at times when divert bases were closed due to bad weather or were unavailable due to political considerations, made the rendezvous and refueling critical both to the success of the mission and the safety of the receiver and crew. The aerodynamic dissimilarity of the subsonic KC-135Q and its triple-sonic receiver dictated a precise rendezvous, and the actual air refueling was conducted at the limits of each airplane’s operational envelope.

There were two types of rendezvous used by KC-135Qs during missions in support of A-12s and SR-71s. Other than differences in timing, these two procedures were identical. The first of these, known as the ‘cold’ rendezvous, was used when the receiver was subsonic prior to the air refueling, such as for the initial onload after takeoff or during pilot qualification training. The ‘hot’ rendezvous was used when the receiver was supersonic prior to the air refueling, such as during an operational mission or ferry flight. Under extreme or degraded conditions such as poor visibility or radio silent operations, KC-135Qs dumped a small amount of fuel, leaving a visible trail for the receiver crew to follow to find the tanker (a practice not limited to A-12 or SR-71 operations but used as needed by all tankers). The KC-135Q’s strobe lights helped the receiver pilot spot the tanker in the final stages of the rendezvous, reducing unnecessary delays and radio transmissions during the closure to contact.

SR-71 refueling was particularly delicate and required considerable skill by the receiver pilot to maintain visual and physical contact during refueling. On Jun. 17, 1970, for example, SR-71A 61-7970 collided with the horizontal stabilizer of KC-135Q 59-1474 during air refueling over Texas, probably the result of passing through jetwash or clear air turbulence. The SR-71 lost its nose and became uncontrollable; the crew ejected safely. Although one of the tanker’s horizontal stabilizers was almost completely separated from the aircraft, the tanker crew was able to maintain control, pinpoint the downed SR-71 crew, and return safely to Beale AFB for recovery. Normal refueling for the SR-71 was conducted at 355 KIAS — red-line speed for the KC-135Q — and at block altitude of FL260—FL270, an altitude lower than SR-71 crews preferred but as high as a KC-135Q ‘fat with gas’ could go while maintaining 355 KIAS. Near the end of the air refueling, the SR-71 was at the limits of its subsonic heavy weight performance capability, and often used one afterburner in order to stay in contact with the tanker. Tests with KC-135Rs showed a 20 KIAS increase in the tanker’s maximum speed, allowing the SR-71 to refuel at 375 KIAS, a considerable improvement, especially during heavy weight operations. Refueling operations with KC-10s increased the base refueling block up to 33,000ft (10,058m) and the speed to Mach 0.88.

According to an unclassified SAC history, the first KC-135Q deployment to Southeast Asia involved ten KC-135Qs relocating from Beale AFB to Kadena AB between Sep. 27 Oct. 30, 1967. As each KC-135Q arrived at Kadena AB, a local KC-135A would depart for the 4258th SW at U-Tapao RTNAB. These first KC-135Q missions from Kadena AB were reportedly `bomber refueling missions’. In fact, KC-135Qs were quite active throughout 1967 in the trans-Pacific deployment of the A-12s to Kadena AB. The first A-12 overflight mission of North Vietnam —Operation BLACK SHIELD — took place on May 31, 1967. CIA pilot Mele ‘Mel’ Vojvodich flew A-12 Article 131 (60-6937) over Hanoi, Haiphong, and Dien Bien Phu (Mel had previously flown RF-86F HAYMAKER overflights of the USSR and PRC). The mission required a pre- and post-overflight refueling with KC-135Qs. Given that this was four months before the first SAC-acknowledged deployment of KC-135Qs to Southeast Asia, it is clear that either SAC historians were unaware of the CIA A-12 mission support or they were publishing disinformation. ‘Bomber refueling missions’ indeed! The final A-12 BLACK SHIELD mission was on Mar. 8, 1968. A-12s had also overflown North Korea three times in 1968 during the USS Pueblo incident, all of which used KC-135Qs for air refueling.

Two weeks after the final BLACK SHIELD mission, its successor had its first overflight of North Vietnam, again with the assistance of KC-135Qs. USAF Major Jerome ‘Jerry’ O’Malley and Captain Ed Payne flew SR-71A 61-7976 on the initial GIANT SCALE mission from Kadena AB in a classic reconnaissance sortie, including a ‘goat rope’ finale. Following refueling immediately after takeoff, the SR-71 overflew Hanoi and Haiphong before refueling from two KC-135Qs (plus an airborne spare) over Thailand prior to again overflying North Vietnam, this time close to the DMZ to identify supply efforts related to the siege of Khe Sanh. Approaching Kadena AB, the weather deteriorated and, despite a low visual approach, O’Malley had to divert to Ching Chuan Kang AB (CCK) on Taiwan. Escorted and refueled by two air spare KC-135Qs, the SR-71 landed and then ‘hid’ between the two tankers on the ramp while waiting for a hangar to be vacated in which the SR-71 could be parked.

This first appeared in Aviation Geek Club here.