The Caribou was, by the mid-1960s, the largest fixed-wing aircraft in the US Army inventory, and that was the problem. The Air Force regarded tactical airlift with fixed-wing aircraft as its own mission and saw the Army’s growing fleet of Caribous, and the larger DHC-5 Buffalo on order, as a challenge. The Army, for its part, wanted an unrestricted helicopter force, especially heavy-lift types like the CH-47 Chinook.

In April 1966 the two chiefs of staff, General Harold K. Johnson and General John P. McConnell, signed an agreement that settled the matter. The Army gave up its claim to fixed-wing tactical airlift, including the Caribou, and the Air Force dropped its objections to Army helicopters. On 1 January 1967, under the transfer known as Operation Red Leaf, six Army aviation companies were inactivated and their aircraft passed to six newly activated USAF Troop Carrier Squadrons, the 457th, 458th, 459th, 535th, 536th and 537th. The Caribous were redesignated C-7A and placed under the 483rd Troop Carrier Wing and the 834th Air Division, flying exactly the same missions with new crews.

Australia ordered its first Caribous in 1963, and in July 1964 the RAAF Transport Flight Vietnam deployed to Vung Tau with seven aircraft. On 1 June 1966 it became No. 35 Squadron. Assigned to the US 834th Air Division, the squadron flew cargo, passenger and medical evacuation sorties throughout South Vietnam for Australian, South Vietnamese and American forces. Its radio callsign, “Wallaby”, gave it the nickname Wallaby Airlines, and the Australian War Memorial records it under that name.

The work was dangerous. Caribous often flew at low level into contested areas, were fired on several times and had aircrew wounded. Two aircraft were destroyed in accidents on poor strips and in bad weather, and another was destroyed by Viet Cong mortar fire at Thất Sơn in 1970. US commanders sent personnel to study the squadron’s methods, and its members received eight Distinguished Flying Crosses among other awards. No. 35 Squadron flew its last mission on 13 February 1972 and left on 19 February, the last RAAF unit to leave Vietnam.

• DHC-4: basic STOL transport.
• DHC-4A: version with increased take-off weight, the standard export model.
• YAC-1: five aircraft for US Army evaluation.
• AC-1 / CV-2A: first US Army production batch of 56, redesignated in 1962.
• CV-2B: second Army batch of 103 with strengthened structure.
• C-7A / C-7B: USAF designations for the 144 Army aircraft transferred in 1967.
• CC-108: Royal Canadian Air Force designation.
• Tp 55: one aircraft evaluated by the Swedish Air Force, 1962–65.
• DHC-4T Turbo Caribou: civil conversion with Pratt & Whitney Canada PT6A-67T turboprops by Pen Turbo Aviation.

After military retirement many Caribous went to civil operators in places with short airfields and few roads: the highlands of New Guinea and Papua, Ecuador’s oil fields, Indonesia, Gabon and northern Canada. Ansett-MAL flew one in the New Guinea highlands from the early 1960s, and the municipal government of Puncak Regency in Papua bought one as recently as 2016. The attraction was simple: a payload of about four tonnes delivered to a strip that otherwise only a helicopter could reach.

The costs are those of any large piston twin. The R-2000s burn avgas, which is expensive and hard to find in remote regions, and need regular overhauls. That is why conversions such as the DHC-4T Turbo Caribou, with PT6A turboprops burning jet fuel, appeared. The hourly figure we give is an estimate with a stated basis, not a published number.