Republic F-12 Rainbow

The F-12 Rainbow was a long-range, four-engine aircraft with an onboard capability for developing film; only one prototype was built and the model was one of only two recon-specific types developed during World War II (the other being the Hughes F-11). The F-12 was redesignated the XR-12 when the US Army Air Forces separated from the US Army.

Only two US specialized photographic recon aircraft were developed during the war: the Hughes F-11 and the Republic F-12. The former was a twin-engine aircraft designed by aviation pioneer, industrialist, and film producer Howard Hughes. Two F-11s were built with competitive powerplant arrangements; Hughes crashed and was almost killed flight testing one of these prototypes. The F-12 Rainbow was a long-range, four-engine aircraft with an onboard capability for developing film; only one prototype was built. Neither aircraft entered production or service.


In many respects, high-altitude photography offered the most important means of intelligence collection during the 45 years of the Cold War. During World War II, aerial photography had been used mostly to locate enemy forces for targeting and for post-attack bomb damage assessment. Initial post–World War II applications of high-altitude photography were primarily for domestic photomapping and surveying for highway construction and mineral and oil exploration.

In Operation Leopard (1948), USAF camera-fitted RB-29s crossed the Bering Strait to take oblique photos of the Chukotski Peninsula in the Soviet Far East. This area was thought to possibly contain Soviet bomber bases targeted against North America. Subsequent USAF peripheral missions of this kind in the Far East had codenames such as Overcalls, Rickback, and Stonework. They could confirm no bomber bases, but they did detect the beginnings of a Soviet air-defense system. The RB-29s could fly missions up to 30 hours in duration without aerial refueling.

The air force needed both medium- and long-range reconnaissance aircraft, the latter to overfly the Soviet Union in advance of potential strategic bomber strikes and for post-strike damage assessment. General Curtis E. LeMay, who had taken command of the new Strategic Air Command (SAC) in October 1948, was particularly dissatisfied with the air force’s strategic reconnaissance capability.28 In the late 1940s, only RB-29s were available for that role.

Improved strategic reconnaissance aircraft were proposed. At first, modifications of existing bomber aircraft were undertaken with the RB-50 following the RB-29. Two new aircraft were seriously considered for the strategic reconnaissance role: the Republic F-12 Rainbow (a four-engine piston aircraft) and the RB-49 version of the Northrop B-49 Flying Wing (a six-engine turbojet aircraft of radical design). Air force plans called for 73 F-12s to be built by 1952, but that project was soon dropped in favor of the Flying Wing. Eventually, the entire B-49 program—both bombers and recon aircraft—was terminated.

Further cancellations took place. In May 1949, work was halted on the RB-54, which would have been a reconnaissance variant of the proposed B-54 upgrade of the B-50 Superfortress. All of these programs were cancelled in favor of the advanced jet-propelled bombers already being planned and tested, as well as the very-long-range B-36 Peacemaker. The air force now concentrated on specialized reconnaissance variants of the giant B-36. This aircraft would be ideal for the post-strike reconnaissance role, at least in the nearterm (early to mid-1950s).

With only four exceptions, all US military spyplanes have been adopted from existing military or civilian aircraft. The exceptions were the World War II–era Hughes F-11 and Republic F-12 Rainbow, and the Cold War–era Lockheed U-2/TR-1 Dragon Lady and the A-12 Oxcart/SR-71 Blackbird. The reasons for adopting existing designs are lower development cost, earlier deployment time, and more efficient and economical support in the field. The decision to employ primarily modified bomber aircraft for the strategic recon role was due in part to the demands of General LeMay, head of SAC from October 1948 to June 1957 and Chief of Staff of the Air Force from 1961 to 1965. General LeMay believed that using modified bombers would simplify logistics, training, and operations. Indeed, he rejected the proposed U-2 spyplane for SAC use in favor of adopting existing bomber designs.


During World War II, the army worked to develop a purpose-built reconnaissance airplane that could fly high and fast enough to avoid conventional enemy anti-aircraft and fighters. Two distinctly different aircraft were brought to the prototype stage to meet the army’s requirements. Hughes Aircraft Company offered the twin-engine XF-11, while Republic Aviation chose a bigger, and ultimately faster, four-engine platform.

The Republic XF-12 program was initiated in mid-1943 as Allied commanders began to plan bombing attacks on the home islands of Japan. The new photorecon airplane was required to cruise at over 400 miles per hour (644 kilometers per hour), operate at 40,000 feet (12,192 meters), and fly over 4,000 miles (6,437 kilometers). Both the XF-11 and XF-12 would take advantage of the development of the new large and powerful Pratt & Whitney R-4360 engine, generating over 3,200 horsepower, to attain these lofty requirements.

The Army Air Forces assigned Republic’s photo aircraft the XF-12. The X stood for “experimental” and reconnaissance projects received an F mission designator (for “photo,” or “foto”). As the USAAF became the US Air Force, and the pursuit designation gave way to F for “fighter,” the plane was re-coded XR-12, the R standing for “reconnaissance.”

The plane’s company and official military nickname was Rainbow. Aviation Magazine dubbed the aircraft the “Flying Photo Laboratory” in their December 1945 issue.


The primary concern of Republic engineers was uncompromising aerodynamic design for their new aircraft. The plane’s bullet-shaped fuselage, tightly cowled engine nacelles, and thin, straight-tapered wings helped keep performance projections high. Even the plane’s exhausts were deliberately routed directly aft, allowing escaping gases to add a small amount of thrust.

The plane’s sleek, clean design made it look like a swift-swimming shark or a graceful bird of prey. Along with the Lockheed Constellation, many judge the XF-12 to be one of the best-looking aircraft of the era.

The XF-12’s pilots sat in a long, pointed Plexiglas nose. Behind, the plane’s slender 10 foot, 3 inch (3.1 meter) fuselage could hold a plethora of photographic equipment. Electrically heated cameras, both standard and stereographic, could be mounted in arrays in three bays equipped with aerodynamically clean retractable doors. For night missions, the bays could accommodate flash photo bombs to illuminate a photo target. Perhaps most unusual, the big XF-12 carried a fully equipped photo lab, allowing crewmen to develop film while still in flight and have the data ready for analysis immediately upon return to base.

The plane’s four large R-4360 engines were nearly completely covered by sizable propeller spinners and tapered nacelles. Impeller fans pulled cooling air into the cowlings and then released it directly aft, along with the engine exhaust.

The XF-12 was designed to operate unarmed. Theoretically, the plane’s speed and high ceiling would allow it to complete missions without any threat of interference from hostile forces.


Two prototype aircraft were initiated at Republic’s Farmingdale, New York, facility as the war progressed. At the cessation of hostilities, the future of most military aircraft projects was in doubt, but the army informed Republic that they would like to continue with the XF-12.

The first example took to the skies on its maiden flight on 4 February 1946. Both Republic and the army were pleased with the plane’s performance. The sleek XF-12 was one of the fastest large-sized piston-engine aircraft ever built. With speeds of over 400 miles per hour, ceiling beyond 40,000 feet, and a range of 4,000 miles or more, Republic ads touted that the new plane could fly “On All Fours.”

The post–World War II era brought another consideration into play: examples of the plane could be sold to civilian airlines as passenger-carrying aircraft. With upcoming military production keeping the price per plane low, Republic offered a 46-passenger aircraft based on a stretched version of the army aircraft. The airliner could make the flight from New York to London two hours faster than the competition. American Airlines and Pan American Airways signed contracts to buy civil versions, designated RC-2.

In 1947, as the new US Air Force, the military changed the designation of their airplanes too. The XF-12 became the XR-12.

In 1948, the second XR-12 completed Operation Bird’s Eye. The aircraft and its crew began shooting film off the coast of Los Angeles and photographed a continuous picture (over 390 end-to-end photographs joined in a continuous strip) across the entire country to Long Island, New York.

The military eventually cancelled the program when it found that other, existing platforms (as well as new jet aircraft) could tackle their long-range reconnaissance mission needs. When the air force backed out, the cost of civilian versions of the aircraft skyrocketed, causing airlines to abandon the design as well. In the end, Republic built only two aircraft.


Retired. The first of the two prototype aircraft, serial number 44-91002, was severely damaged during a landing test on 10 July 1947. The plane went back to Republic for extensive repairs and then was put back into service. The XR-12 was officially retired from air force testing and was turned over to the Aberdeen Proving Ground to be used as a gunnery target in 1952.

The second Rainbow aircraft, serial 44-91003, was lost after an in-flight engine explosion in 1948. Five of the seven air force crewmen were able to bail out. The plane crashed in the Choctawhatchee Bay near Eglin AFB, Florida.



ENGINES: 4x Pratt & Whitney R-4360-31; 3,250 hp each

WEIGHTS: Empty: 68,000 lb (30,844 kg) Maximum: 101,400 lb (45,994 kg)

LENGTH: 93 ft 10 in (28.6 m)

WINGSPAN: 129 ft 2 in (39.4 m)

HEIGHT: 28 ft 4 in (8.6 m)

SPEED: 470 mph (756 kph)

CEILING: 45,000 ft (13,716 m)

RANGE: 4,500 mi (7,242 km)