DHC-4 Caribou, Projects & Variants

Beginning in 1961, Army Security Agency soldiers operated in Vietnam, conducting reconnaissance and interception of Viet Cong radio transmissions. Since the ASA could not be officially present in Vietnam, the units bore the code name Radio Research (RR). As of April 1962, the ASA began using aircraft to directionalize the signal. After unsuccessful attempts with the H-19 helicopter, the choice fell upon the U-6 Beaver, followed by the U-8 Seminole. However, both of these types could only locate the radio signal. A single CV-2B Caribou [62-4147, c/n 82] was therefore modified by the U.S. Army in 1965 as the Pathfinder SIGINT/ELINT reconnaissance platform and designated RCV-2B, being the first aircraft whose crew both could intercept and record transmissions. The story of that one-of-a-kind aircraft would be all but forgotten were it not for the precious testimony left online by members of its crew.

Pathfinder's assignment

In January 1963, a month after its acceptance by the US Army, [62-4147] was transfered to the Army Security Agency (ASA) at Fort Monmouth, New Jersey, where it was modified (equipped with HF DF) and assigned to Pathfinder duties. Three years later, in January or February 1966 (depending on sources), the RCV-2B was assigned to the 3rd Radio Research Unit at Tan Son Nhut Airport, in Ho Chi Minh. With the increasing number of personnel and equipment, however, the ASA in Vietnam was reorganized in June 1966. For the aviation units, an entire aviation battalion, the 224th Aviation Battalion (Radio Research), was created, which had four companies: 138th Aviation Company (RR), at Da Nang; 144th Aviation Company (RR), at Nha Trang; 146th Aviation Company (RR), at Tan Son Nhut (where the RCV-2B operated from); and 156th Aviation Company (RR), at Can Tho. According to one crew member, however, Pathfinder did not fall under any unit in Vietnam and was directly subordinate to the US ASA Pacific headquarters. This could be explained by the fact that the aircraft operated throughout South Vietnam, while the 146th Aviation Co. (RR) was assigned to III.CTZ. Whatever the case, it certainly used the facilities of the 146th Aviation Co. (RR).

Configuration and specific equipment

Pathfinder's crew consisted of eight men - pilot, copilot, flight engineer, four ASA operators and a mission controller. Flights usually lasted 4 hours, after refueling they could stretch up to seven hours. "Pathfinder" operated throughout South Vietnam, occasionally flying beyond its borders to Cambodia, Laos or North Vietnam. There were four positions in the fuselage for operators who could record and intercept radio transmissions in the short and very short wave bands, or locate radio transmissions in the short wave band. There was also a teletypewriter on board for secure air-ground data communication. Since the equipment used up more electrical power, the two turbines of an electric generator were placed under the wings. An old World War II sight was mounted in the cabin floor to record the exact position on the ground. The enemy's position could also be verified using an infrared camera. The pilots had a Sperry C-12 compass system, a Doppler radar and a Decca navigation system at their disposal. This particular system was quite old (it ceased to be used in Vietnam in 1968), but its main purpose was to indicate the aircraft's position (which was important for determining the position of the focused radio signal) while actual navigation itself was only a secondary use. Finally, a Polaroid camera was carried on board for taking instant pictures of the pilot's instrument panel. The photos of the panel were then placed on a large map board with signal search.

A spectacular incident

On Sept. 20, while performing an intelligence intercept operation over North Vietnam, slightly north of the Demilitarized Zone (DMZ), at about 5,000 ft. altitude, Pathfinder started to take ground fire from an NVA gun emplacement situated on a 2,000 ft. mountain. A 37mm anti-aircraft hit the tail, while the belly of the airplane was peppered with .30cal. at extreme range. The pilot immediately banked towards the DMZ, being able to skillfully turn the plane without rudder function, compensating by alternating the prop pitch. He subsequently landed the crew safely without any combat injury on the PSP-runway at U.S. base Dong Ha, a few kilometers below the DMZ.

At Dong Ha everyone piled out and laid on the PSP, looking at the belly. Nothing had penetrated the skin, but the bottom of the aircraft looked like it was attacked by someone with a ball pen hammer (unfortunately, no photos of the belly were taken). Suddenly they noticed a group of Air Force people staring at the tail with their mouths hanging open, realizing only then the damage sustained. After a few nervous cigarettes, the pilot gave the crew the option of returning to Phu Bai in the Caribou, or riding in the SAR helicopter that would be escorting them. Each and every one of them chose to climb back in the Caribou for the return to Phu Bai. (A much more detailed account of the whole episode can be found in the second link below.)

After being repaired, Pathfinder was assigned to the 146th Aviation Co. (RR), but its career was short-lived — not because of this or any other accident, but by an agreement between the Army and the Air Force, whereby the Army pledged to hand over all medium transport aircraft to the Air Force while the USAF in return would limit the operation of helicopters. The agreement, under operation "Red Leaf", was to be fulfilled by the end of 1966. The handover, of course, also concerned the RCV-2B, which was to be transfered in "normal" configuration, i.e. as a regular transport machine. Its pilot, Capt. Dexter, was given the task of developing instructions on what needed to be done to return [62-4147] to a "normal" configuration. However, Dexter argued that the modifications were so extensive that they could not be removed in Vietnam. Besides, the Army wanted to use Pathfinder's capabilities as long as possible. This somewhat delayed the handover, but the RCV-2B, now a C-7A, was finally turned over to the USAF on May 31, 1967, and transfered in August to McClellan AFB (Air Force Logistics Command) in Sacramento, CA for repairs. Eventually, it returned to Vietnam, being assigned in 1968 to the 457th Squadron at Can Ranh Bay (Vietnam Tail code "KA"). After suffering a minor gear-up landing in 1971, the aircraft was transfered on March 31, 1972 to the 377th ABSWG/310th TAS at Phu Cat, then handed over to the South Vietnam Air Force's 427th Transport Squadron later that year, under the Military Assistance Program (Tail code "GD"). Nothing is known of its later whereabouts.

Redesignation

The question of the aircraft's redesignation after its transfer to the USAF is tricky. First of all, the notion that CV-2A aircraft became C-7A while CV-2Bs were redesignated as "C-7B" doesn't hold water when you take a close look at the detailed list of all Caribou aircraft and their individual histories. Indeed, the latest version of dhc4and5.org's so-called "Caribou Roster" (Revision #13) does not include a single "C-7B" aircraft! And so, if we are to believe that site's research (and they are the ultimate source on all DHC-4/DHC-5 aircraft, after all), absolutely every remaining Army Caribou, whether AC-1/CV-2A, or AC-1A/CV-2B, was redesignated in 1967 as a USAF C-7A (with the exception of the YAC-1 prototypes, which became YC-7A). Even the designation "VC-7A", supposed to have been used for several examples returned to the US Army National Guard, is apparently totally apocryphal!

Also, there are several sources alluding to the RCV-2B becoming the "RC-7B" but that too seems apocryphal 1. Being eventually returned to transport status, [62-4147] just became a C-7A like any other. And even if it had been temporarily designated with an "R" modifier until the changes could be made (there was no "E" modifier yet), surely it would have been an "RC-7A" not a "B"... but even that designation can't be found anywhere! All of this shows the importance of always checking the facts instead of repeating age-old mistakes, even when the seem to emanate from serious sources.

1 When the DoD finally allocated RC-7B, 40 years later, for another De Havilland Canada aircraft (the DHC-7 Crazy Hawk), it caused quite a stir among designation buffs because it made little sense to give the four-engine DHC-7 the same designation as the earlier, twin-engine DHC-4 (someone must have realized it was not quite right, and Crazy Hawk became the EO-5C on August 15, 2004).
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