Southern California's masters of airlift, part 2: the C-132 and C-133 Cargomaster

The second post in my multi-post series about Douglas/McDonnell Douglas strategic airlifters focuses on the first-generation of gas turbine-powered heavy-lift transport planes conceived by Douglas in the 1950s (by which time long-range airlift was becoming enshrined as a pillar of US strategic military aviation policy). As explained in my previous post on the C-74 Globemaster and C-124 Globemaster II, Douglas had tinkered with re-engining the C-124 with turboprop engines, producing the YC-124B (aka C-127) prototype turboprop airlifter, but test flights revealed that the operating range of the YC-124 fluctuated with altitudes because the C-124 airframe was unpressurized (although the YC-124B had a pressurized cockpit). Thus, this post will focus on Douglas designs for turboprop-powered heavy-lift aircraft, including the C-133 Cargomaster and the unbuilt C-132 project.   

Top: Desktop model of the C-133 Cargomaster at the Western Museum of Flight
Bottom: C-133B Cargomaster (serial number 59-0529) flying over San Francisco Bay, 1960 

After recognizing the deficiencies of the YC-124B in terms of operating range at varying altitudes, the Douglas Aircraft Company realized that pressurizing the entire C-124 design would require a panoply of design changes, including fixing the auxiliary floors in the down position and latching them to form a tension tie across the fuselage (effectively eliminating the ability to haul outsized cargo), and reskinning sections of the fuselage with thicker-gauge aluminum. Douglas therefore envisaged a new large strategic transport design, the Model 1324 (dubbed 'C-124X' internally by Douglas), which retained the wings of the YC-124B/YKC-124B but differed in having a circular cross-section fuselage. Early designs for the Model 1324 had the nose ramp and tail shape of the C-124, but later proposals had the ramp moved to the tail section to enable air-dropping of cargo. Nine Model 1324 configurations were proposed, all varying in turboprop engine options, wing flap types, and gross weight levels. Despite the improvements in wing and fuselage geometry, the cargo deck of the Model 1324 was far from truckbed height, so on March 24, 1953, the Model 1324 was abandoned in favor of the Model 1333, which had a new shoulder-mounted wing that had a revised airfoil, thickness, twist, and leading and trailing edge sweep angles, as well as the fuselage being lowered to the ground so that the cargo deck was low enough for trucks and military vehicles to be loaded into the aircraft. Other features of the Model 1333 included elimination of the secondary deck, all passenger provisions and pressurization. 

Douglas C-133A (serial number 56-2010) at RAF Lakenheath, Suffolk, England, in May 1969

On August 10, the Model 1333 was given the designation C-133 by the US Air Force, and on April 23, 1956 the C-133 made its first flight; no C-133 prototypes were ever ordered because no other aircraft offering the immediate prospect of the performance and cargo capabilities of the C-133. Operational deployment of the C-133 Cargomaster with the Military Air Transport Service commenced in August 1957, and a total of 50 C-133s (35 C-133As and 15 C-133Bs) were built and deployed. Although the C-133A was not specifically designed to carry ICBMs, the C-133B had rear cargo doors modified to open to the side, making ICBM loading much easier. Douglas in May 1959 offered a variant of the C-133B with improved cargo capacity, an aerodynamically efficient and symmetrically tapered rear fuselage, and four Allison T61 turboprops, known as the Model 1476, but this design did not progress beyond the drawing board. During their service life, C-133s ferried ICBMs to and from missile silos in the US as well as Atlas, Titan, and Saturn rockets to Cape Canaveral to be used to launch Mercury, Gemini, and Apollo manned spacecraft, and they helped transport war material and troops to US bases in Western and Central Europe while proving invaluable in the Vietnam War. The C-133 served with MATS until 1971, when it was replaced by the Lockheed C-5 Galaxy.

Top: A desktop model of the proposed cargo pod-carrying variant of the Douglas Model 1240
Bottom: An artist's conception of the C-132 heavy airlifter in flight

It would not be possible to complete my discussion of Douglas turboprop-powered strategic airlifters without mentioning a number of Douglas heavy-lift aircraft designs that were conceived in parallel with the C-133 but never reached the hardware phase. In response to the XC-Heavy requirement issued by the US Air Force in early 1951, Douglas proposed a military transport version of twin-boom Model 1240 (similar to the company's Model 1211J turboprop-powered strategic bomber project in having a very high-aspect-ratio swept wing), which had one central and two auxiliary cargo pods under the wing center section. The Model 1240 pod-carrying variant had a wingspan of over 200 feet, and power was to be provided four turboprops and two auxiliary turbojets. The cargo pod-carrying variant of the Model 1240, however, was not proceeded with because the US Air Force judged the price of the design to be a 6.9% drag penalty compared to a conventional cargo plane. Douglas eventually returned to the drawing board to fine-tune its design for the XC-Heavy contest, and after investigating a spree of somewhat smaller designs with new engine options, it opted for a conventional transport design with a shoulder-mounted back swept wing, the Model 1814. On December 5, 1952 the Air Force selected the Model 1814 for full-scale development and designated it XC-132 in April 1953. The C-132 fuselage had a 'double-lobe' cross section to accommodate two decks, the upper part being pressurized forward of the wing-box for the flight crew. The lower part of the fuselage would accommodate all military vehicles, equipment, or special weapons, and provisions were made to anchor the cargo netting to the sidewalls of the bay. The C-132 was 183 feet 10 inches (56.03 meters) long with a wingspan of 186 feet 8 inches (56.90 meters) and the ability to carry 100,000 pounds (45,359 kg) of cargo, while power was to be supplied by four Pratt & Whitney T57 turboprops each delivering a total of 15,000 shp (11,000 kW). Douglas also planned a tanker variant of the C-132 as the KC-132, which was to be 12,689 lb (5,755 kg) heavier than the C-132 with a total fuel load of 290,000 lb (131,542 kg), and one C-132 variant, the Model 1905, was envisaged in December 1955 with a pressurized upper aft deck compartment to accommodate 100 troops and a more powerful version of the T57. In 1953, a full-scale mock-up of the C-132 was built at the Douglas plant in Santa Monica, with inspection of the mock-up conducted in early 1954. Two YC-132 prototypes were ordered, and the T57 turboprop planned for the C-132 was tested aboard a C-124 Globemaster II in October 1956. Plans called for the construction of the C-132 prototypes to begin in May 1957, with final assembly taking place in June 1958, rollout in May 1959 and the first flight in August. However, on March 29, 1957, the US Air Force cancelled the C-132 program before construction of the prototypes could begin due to budget cuts, concerns about the small size of the cargo space relative to the overall size of the aircraft, expected difficulties in loading ICBMs into the C-132, and the cancellation of the T57.  

References:

Cox, G., and Kaston, C., 2019. American Secret Projects 2: U.S. Airlifters 1941 to 1961. Manchester, UK: Crécy Publishing.

Gunston, B., 1991. Giants of the Sky: The Largest Aeroplanes of All Time. Sparkford: Patrick Stephens Limited.

Taylor, C., 2005. Remembering an unsung giant: the Douglas C-133 Cargomaster and its people. Olympia: Firstfleet Publishers. ISBN 978-0977676200.