The KA-6D was an A-6A modified for use as aerial refueling tanker. A total of 90 A-6As were converted into KA-6D tanker Intruders.
The Navy's experience with jet aircraft in the Korean conflict led to a requirement for a low-level attack bomber that could deliver ordnance against moving and fixed sea and land targets in all-weather and darkness. It was to be subsonic and capable of delivering nuclear as well as conventional ordnance thus being useful in both nuclear retaliatory and conventional conflicts. Originally designated A2F-1 and changed to A-6A in the DOD uniform designation system, this aircraft was first accepted by the Navy in February 1963 by VA-42.
In 1968 Grumman got a go-ahead from the US navy to build a tanker variant of the Intruder. It was designated KA-6D and flew for the first time on April 16, 1970. The Digital Integrated Attack Navigation Equipment (DIANE) system was taken out, the aircraft was completely rewired, the internal fuel tanks were replaced and the wings were reworked. For navigation, an Omega navigation system was put in. The transferrable fuel was stored in four underwing tanks and sometimes in a large backup fuel pod under the fuselage. The second crew-member was responsible for filling up the receiving aircraft by reeling out a hose from the back of the aircraft. The receiving aircraft would then fly its refuelling probe into a basket-like funnel at the end of the hose. This is known as the probe-and-drogue system.
The Navy did its own refueling with Douglas KA-3 tankers and later with Grumman KA-6 tankers. The KA-3 could deliever 29,000 lb of fuel at 460 miles, about 2.2 full F4J tanks. The KA-6 only delivered half as much fuel, and the S-3 carried even less. Strike forces launched from aircraft carriers in the Gulf of Tonkin were accompanied by tankers for a final refueling before they went to the target. Tankers were held in standby orbits for attackers returning from the target, and a tanker was always in orbit over the aircraft carrier in the event a returning airplane, almost out of fuel, missed its "trap" and had to circle for a second attempt at landing.
In spite of Navy KA-6 and KS-3 tankers flying more than 1,000 refueling sorties during the Persian Gulf War, Navy airplanes depended on Air Force KC-135s for refueling. Somewhat more than 30 percent of the KC-135 aerial refueling in that war was performed on behalf of the U.S. Navy.
Normally in Vietnam operations, aircraft carrier planners found it necessary to put two KA-3/KA-6 tankers aloft per cycle, "dispensing maximum" fuel to launching Phantom IIs, then "consolidating" the two tankers; one then landed, short cycling, and the other full cycled.
The KA-6D theoretically could be used in the day/visual bombing role, but it apparently never was, with the standard load-out being four fuel tanks. Because it was based on a tactical aircraft platform, the KA-6D provided a capability for mission tanking -- the ability to keep up with strike packages and refuel them in the course of a mission. A few KA-6Ds went to sea with each Intruder squadron, and the retirement of the aircraft left a gap in USN and USMC refueling tanker capability. The USN S-3 Viking also has an aerial refueling capability, but its performance and fuel capacity effectively limit it to the role of recovery tanker. The loss of mission tanking capability was only later remedied by the new F/A-18E Super Hornet, which can act as a mission tanker.
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