The C-7A (DHC-4) is a light tactical transport designed for operation in the most primitive of conditions. Capable of carrying passengers, litter patients, or cargo, it can land and take off on unprepared surfaces of less than 1,000 feet in length. Its cargo area was unobstructed and had floor rollers to permit airdrop of equipment or personnel.
Originally designed by deHavilland of Canada in direct response to a U.S. Army request for a STOL transport with similar load capacity to the CH-47 helicopter, the DHC-4 was an extension of the Army’s long association with deHavilland. The Army had previously purchased both DHC-2 Beaver (L-20) and DHC-3 Otter (U-1) aircraft from deHavilland.
As had been their custom in the past, deHavilland designed the aircraft for both military use and civilian airworthiness certification. The first prototype flew on 30 July 1958. Because the development program was rushed to meet U.S. Army demands, the very early aircraft were modified substantially during their initial testing to evolve into what would become the DHC-4.
With an Army designation of AC-1, the first Caribou pre-production aircraft were flown by an operational unit in 1961. In 1962, the Army redesignated the aircraft to CV-2A. Many modifications continued to be made as production progressed and there was eventually a CV-2B model, which included a nose radome, housing a weather radar antenna. Because of the wide range of production variations and later retrofits of previous aircraft, some of the specifications are hard to pin down. Each aircraft had its own “personality” and idiosyncrasies.
Published records show that a total of at least 159 aircraft were purchased by the U.S. Army. During the mid-1960s, what could only be described as a “turf war” took place between the U.S. Army and U.S. Air Force. The Air Force argued that it was the military branch tasked with providing air resources and that it should rightfully be operating the CV-2. In 1966, that debate was concluded with the transfer of all the Army Caribou units in Vietnam to the Air Force. The Air Force redesignated the Caribou to C-7A and rapidly took over all in-country operations. Initially, there were six C-7A squadrons; two at Vung Tau, two at Cam Ranh Bay, and two at Phu Cat. By the end of the war, combat losses had reduced the squadron count to five; four at Cam Ranh and one at Phu Cat.
The C-7A, as operated by the Air Force, is described as an unpressurized, high wing, Short Take Off and Landing (STOL) aircraft powered by two Pratt & Whitney R2000-7M2 radial engines. The powerplants were equipped with engine-driven single-speed superchargers and developed 1,450 BHP at 2,700 RPM under standard day conditions. The engines were fitted with three blade Hamilton-Standard full-feathering, reversible hydromatic propellers. The engines were also fitted with two exhaust augmentor tubes over the top surface of the wing behind each engine. These augmentor tubes, open at the front, served to draw cooling through the nacelle and actually added to the total thrust of the powerplant.
The cargo compartment was unobstructed and 6 feet 3 inches high, by 6 feet 2 inches wide, by 28 feet 9 inches long. The cargo floor had two rows of rollers to facilitate handling of heavy, palletized cargo and would accommodate a standard 463L aluminum cargo pallet. The rear cargo door opened inward to leave an unobstructed opening for cargo airdrops. The Vietnam aircraft had their deicing systems and cabin heaters removed and had no crew oxygen system. This latter fact limited the maximum altitude to well under the capabilities of the aircraft.
The C-7A was used to move people and materiel into forward areas, where short, unprepared strips were the norm. They were almost always operated under Visual Flight Rules (VFR) or “Special VFR,” but were fully equipped instrument aircraft. Typical cargoes were fuel (gasoline, diesel fuel, and JP-4), munitions (small arms ammunition, 2.75 inch aircraft rockets, 105mm, 155mm, 175mm, and 8 inch howitzer projectiles), food (widely varying from very conventional American steak and chicken, to live pigs, chickens, ducks, and eels for the ARVN troops), passengers (U.S. military, RVN military, RVN civilians, and even NVA POWs), and sadly, bodies. Most of the destination airstrips of the C-7A in the 1971 time period were along the borders of Laos and Cambodia with South Vietnam and were firebases or Special Forces outposts (U.S., ARVN, and Montagnard).
The Caribou was a workhorse that went from sunrise to sunset every day operating in the heat, humidity, dust and mud from the low-lying Vietnamese Mekong Delta to the towering mountain regions of the central highlands.
The C-7A could accommodate up to 32 passengers, 26 fully-equipped paratroops, 20 litter patients, or an 8,740 pound cargo load.
“The maximum speed, range, and service ceiling values given above are the standard data supplied for the aircraft. In this former C-7A pilot’s opinion, however, 187 knots was not even close to achievable with the aircraft I flew. A 1,000 BHP cruise setting yielded about 120 knots and I did not feel that a higher power setting was prudent, given the abuse the engines took daily. Normal cruise for Air Force aircraft was 105 knots with a power setting of 2,000 RPM and 20 inches of manifold pressure. In several instances where weather and high terrain forced a climb above 10,000 feet, I was just about out of steam at 17,000 feet. That may have been due to the much higher than standard day temperature, but I do not believe it would have been possible to get one of our aircraft anywhere near 24,800. The range figures are also optimistic and probably reflect the performance of a factory-new aircraft.”
Source Note: All data and comments were contributed by Peter A. Bird.
deHavilland C-7 Caribou Specifications
|Official Designation||deHavilland C-7 Caribou C-7A Caribou|
|Unofficial Nicknames||‘Bou, Gravel Truck|
|Primary Role||Tactical airlift|
|Original Contractor||deHavilland Canada|
|Wingspan||95 feet, 8 inches|
|Height at Tail||31 feet, 9 inches|
|Engines||Two Pratt & Whitney R2000-7M2 radials|
|Horsepower||1,450 shp each|
|Cruise Speed||121 mph|
|Max Speed||216 mph|
|Range||1,200 nm (could be extended by 1,000 nm with ferry tanks)|
|Service Ceiling||24,800 feet (limited to 10,000 feet by lack of oxygen equipment)|
|Max Takeoff Weight||28,500 pounds (33,000 pounds for ferry operations)|