Designated XF-12, when F stood for 'photo' in the pre-1947 system, and later XR-12, the Rainbow was a high-speed high-altitude reconnaissance aircraft, intended to scout targets over Japan for the B-29s. This may have happened if the programme had started earlier, because when the war ended with the atomic bombings, the first aircraft was only partly complete. Republic still hoped to make the Rainbow into a 46-seat airliner, which they called the RC-2. Their selling point was speed, for which customers would pay a premium. Unfortunately, the expected postwar boom was not immediate and the airlines bought the slower but roomier DC-4 and Boeing 377 instead. An XR-12 was not delivered to the Air Force until late 1948, but crashed on its second test flight. The other Rainbow was sent to a gunnery range.