One of the weaknesses of early jet fighters was their limited range and endurance. The FICON (FIghter CONveyor) project was an early 1950s attempt to extend the range of fighter and reconnaissance jets by having them operate as parasites from B-36 bombers.
On January 19, 1951, Convair was ordered to modify an RB-36F bomber (serial number 49-2707) to carry and recover a modified F-84E Thunderjet. The modified RB-36F was redesignated GRB-36F. The bomb bay of the GRB-36F was extensively modified, and the usual bomb racks were replaced by a retractable H-shaped cradle. F-84E serial number 49-2115 was modified to carry a hook on the upper nose ahead of its cockpit. During the recovery operation, the F-84E was to fly up underneath the B-36 and use its hook to engage a slot in the cradle. The cradle would then rotate down over the fuselage of the F-84E and engage hardpoints on the rear fuselage. Once attached, the F-84E would be pulled upward and nestle underneath the belly of the GRB-36F. Launch was carried out by reversing this process.
The GRB-36F/F-84E combination began its first retrieval and launch tests on January 9, 1952. The first complete cycle of retrieval, retraction, and launch took place on April 23, 1952, followed shortly thereafter by the first composite flight made with the F-84E stored in the bomb bay during both takeoff and landing. The GRB-36F/F-84E combination was delivered to Eglin AFB, Florida in late 1952. From there, the pair made up to 170 inflight launches and retrievals, including night operations.
In 1953, the original YRF-84F (49-2430, the first swept-wing Thunderstreak) was modified and tested for the hook up in flight with a B-36. It had a hook on the nose ahead of the cockpit for engaging the H-shaped trapeze lowered from the B-36, and had a set of hardpoints on the rear fuselage for attachment of the aircraft to the trapeze once it was engaged. In addition, the tailplane of the modified YRF-84F was sharply canted downwards in order to clear the bottom of the B-36 during launch and recovery. The conventional landing gear of the YRF-84F was retained. This aircraft was redesignated GRF-84F.
The success of the tests with the F-84E and the GRF-84F led to a USAF order in the fall of 1953 that 25 RF-84F reconnaissance aircraft be modified to operate as parasite aircraft. These aircraft were redesignated RF-84K. Serials were 52-7254/7278. Ten B-36D bombers were ordered modified to act as motherships, these aircraft being redesignated GRB-36D.
Each of the GRB-36Ds carried an H-shaped cradle in the bomb bay which was used to launch and retrieve the parasite. The GRB-36Ds had their ECM equipment relocated further aft, and all armament save the tail guns was removed. Ten GRB-36Ds with cradles for RF-84Ks were delivered to SAC in February/March of 1955.
The GRB-36D motherships saw limited service with the 99th Strategic Reconnaissance Wing based at Fairchild AFB, Washington, operating in a team with RF-84Ks of the 91st Strategic Reconnaissance Squadron based at nearby Larson AFB. The technical operation of FICON was fairly simple, with the carriers and parasites flying out of different bases. The parasite could either be picked up in midair while enroute to the target area, or could be attached by ground hookup prior to takeoff. Once secured to the GRB-36D mothership, the pilot of the RF-84K could get out of his cockpit and enter the mothership via a catwalk. When it came time for his mission, the pilot could reenter the cockpit of the RF-84K in preparation for launch. Night operations were also possible. In a typical mission, a GRB-36D was to carry the RF-84K out to a 2810-mile radius and launch the parasite at an altitude of 25,000 feet. After completion of the mission, the RF-84K would be recovered by the GRB-36D and returned to base. The range of the two-plane combination was up to 12,000 miles, with all but 2000 miles being the range of the B-36.
Operations with the 91st Strategic Reconnaissance Squadron's Thunderflashes continued until the spring of 1956, when they were quietly abandoned. In retrospect, it seems that the withdrawal of the GRB-36D/RF-84K combination from service coincided with the introduction of the U-2 spyplane into service.
When visiting the Wright Patterson Air Force Base Museum in June of 1992, I noted that the YRF-84F is on display there.
The following RB-36Ds were converted to GRB-36D configuration: 44-92090, 44-92092, 44-92094, 49-2687, 49-2692, 49-2694, 49-2696, 49-2701, and 49-2702.