Built in 1946 as a long-range photo-reconnaissance aircraft, Republic's XR-12 was the fastest multi-engined piston-powered airplane ever built,
reaching a top speed of 450 mph in level flight. The fuselage contained three separate camera compartments with facilites to process film in flight.
Eighteen high-intensity flash bulbs were stowed in a hold in the belly for night photography. The Rainbow had one of the highest power
to weight ratios of any multi-reciprocating-engine airplane. Two prototypes of the Rainbow were built. A derivative airliner design,
the Republic RC-2, was proposed as a high speed transport. One Rainbow crashed on a flight out of Eglin Air Force Base, Florida.
The other one ended up as a target at the Aberdeen Proving Grounds, Maryland.