Nuclear-powered airborne giants from southern California, part 3: Santa Monica's atomic airlifters

In my blogpost on the Lockheed CL-1201 flying aircraft carrier project of the late 1960s, I mentioned that Lockheed worked out a heavy-lift transport variant of the CL-1201 that could carry a massive military payload far bigger than that of the C-141 and C-5, and slightly exceeding the cargo capacity of a number of hybrid airship designs envisaged in the 1990s and early 2000s. However, the California division of Lockheed was not the only manufacturer in southern California to propose a strategic airlifter utilizing a nuclear powerplant. More than a decade earlier, even while the US Air Force was formulating requirements for a nuclear-powered strategic bomber, the Douglas company responsible for the C-74, C-124, and C-133 designs in additional to its prolific dynasty of airliner designs toyed with the idea of a giant nuclear-powered transport aircraft. 

Three view drawing of a twin-fuselage Douglas Model 1875 design study (dated April 20, 1955). An additional side view of the single-fuselage Model 1875 iteration is shown on the lower right corner of the drawing. 

In December 1954, Douglas began tinkering with fitting a nuclear reactor to a strategic bomber when it conceived a nuclear-powered version of the C-132, officially labeled "A.P. Transport" ("A.P." stood for "Atomic Power"). Starting in early February 1955 Douglas investigated design studies for a nuclear-powered heavy-lift aircraft for the Aircraft Nuclear Propulsion (ANP) program under the company designation Model 1875, and after a down-selection of numerous concepts with a diverse array of design configurations, it worked out eight Model 1875 designs in March-April 1955 the first four being exploratory concepts embodying twin-pod, twin-fuselage, twin-boom, and single fuselage layouts. one with twin cargo pods and four turboprops connected to a nuclear reactor in the center fuselage, a twin-boom design with four turboprops connected to a nuclear reactor in the center fuselage, a single-fuselage transport with four turboprops fueled by two nuclear reactors in the inboard engine nacelles, and a six-turboprop design with the two nuclear reactors in the outboard engine nacelles. The twin-pod, twin-fuselage, and single-fuselage Model 1875 designs envisaged in April 1955 measured 181 feet 6.3 inches (55.33 meters) long, and whereas the twin-pod and twin-fuselage proposals had a wingspan of 264 feet 8 inches (80.67 meters) and four turboprops housed in coupled pairs in two nacelles in the wing center section, being fueled by a nuclear reactor in the center fuselage, the conventional single-fuselage design spanned 200 feet (60.96 meters) and had four turboprops, of which the inboard engines were fueled by two nuclear reactors in the wings. Parametric evaluations by Douglas indicated that the conventional single-fuselage proposal was superior to other layouts in weight and aerodynamic drag, and engineers deduced that cruise flight could achieve 60 percent of nuclear reactor power necessary for take-off if the reactor were scaled down to meet the cruise power requirement to allow jet fuel to give supplemental thrust, effectively balancing increased payload with reduced gross weight.

After completing analysis and trade-offs for different Model 1875 layouts, in January 1956, Douglas launched a Detailed Study effort examining a common tube-and-wing layout scaled to different wing aspect ratios, fuselage cross-sections, and overall sizes. Two Model 1875 studies dated February 8, 1956, dubbed Studies No. 4 and No. 5 would have been 200 feet (60.96 meters) long with a wingspan of 323 feet 4 inches (98.55 meters); Study No. 4 had six turboprop engines, of which the two outboard engines were fueled by two nuclear reactors in the wings, while Study No. 5A had four turboprops, with the outboard engines being fueled by two nuclear reactors. In July 1956, Douglas worked out a slightly smaller Model 1875 with a 295 foot (89.92 meter) wingspan and powered by six Pratt & Whitney T57 turboprops connected to two nuclear reactors. The large-fuselage Model 1875 proposals from 1956 with an oversized fuselage would have had a capacity for 572 troops seated on two decks when configured for troop transport, and power for the turboprops of these designs would have been supplied by two AC-300-1 reactors.

A cutaway view of the Douglas Model 1444, a proposal for a C-133 Cargomaster to serve as a testbed for the General Electric X211 (J87) nuclear-powered turbojet.

Given the sheer size of the General Electric X211 nuclear-powered turbojet (military designation J87) being considered for the Model 1875, in February 1958, Douglas worked out the Model 1444 scheme for a C-133 Cargomaster to serve as a testbed for the X211 turbojet. The X211 would be housed in the aft section of the cargo compartment, its jet engines being fed by a nuclear reactor behind the cockpit (whose crew compartment had rudimentary lead and rubber shielding from nuclear radiation). Studies done by Douglas for a nuclear-powered transport under the ANP program ended in August 1958, but although the Model 1875 might have carried troops and military equipment for indefinite periods of flight time without having to stop at air bases to refuel, neither it nor the Model 1444 ever materialized, for March 1961, the ANP program was canceled by President John F. Kennedy. 

References:

Cox, G., and Kaston, C., 2020. American Secret Projects 3: U.S. Airlifters Since 1962. Manchester, UK: Crécy Publishing.