During World War II, due to the range requirements of operating in the Pacific, existing fighters and bombers were being used but were poorly suited to the USAAF's needs.

In August 1943, U.S. President Franklin D. Roosevelt's son, Colonel Elliot Roosevelt, commander of a Lockheed F-5 (a modified P-38 Lightning) "recon" unit, recommended the acquisition of a dedicated high-performance photo reconnaissance aircraft to provide pre- and post-strike target analysis intelligence as well as photo interpretation to better allow commanders to make decisions for bombing raids.

[4] The XF-12 was the fastest aircraft of its day to use four reciprocating engines, and the only one to exceed 450 mph (720 km/h) in level flight[5] Minimizing drag was a primary consideration throughout the design of the XF-12.

When the sliding cowl ring was closed during flight, the cooling air was ducted through the nacelle to the rear exhaust orifice increasing thrust, rather than adding drag as is usually the case.

Research showed that a force roughly equivalent to 250 hp (190 kW) was generated by each engine exhaust during high speed cruise while at altitude.

[7] Each engine featured twin General Electric turbochargers at the rear of the nacelle and for brief bursts of additional power, water-methanol injection.

[4] The first prototype was damaged on 10 July 1947 while undergoing maximum landing weight tests when the right main gear was severed at the engine nacelle.

After bouncing hard and staggering back into the air the test pilot climbed to a safe altitude where excess fuel was burnt off, to lighten the aircraft and reduce the risk of fire.

The pilot landed on the left main gear and the nose wheel and despite losing as much speed as possible before the other wing dropped, the aircraft suffered significant damage.

On 1 September 1948, the second prototype departed the U.S. Air Force Flight Test Center at Muroc, California, and climbed west to its 40,000 ft (12,000 m) cruising altitude over the Pacific before heading east.

It then photographed its entire flight path across the United States on 390 individual 10 in (250 mm) photos each covering 490 mi (790 km), which were jointed to form a continuous 325 ft (99 m) print.

On 7 November 1948, the second prototype crashed while returning to Eglin Air Force Base from a photographic suitability test flight after the number 2 (port inner) engine exploded, causing violent buffeting.

Pratt & Whitney R-4360-59s with only one General Electric turbosupercharger each would replace the R-4360-31s, providing more power at lower altitudes, and fuel capacity would be increased.

The airliner would carry a crew of seven, and the lavishly appointed cabin for 46 passengers would feature pressurization to sea level with air conditioning, an electric galley providing hot meals, and an inflight lounge.