On 1941 April 11, the AAC issued a design competition for an aircraft with a 275 mph (445 km/h) cruising speed, a service ceiling of 45,000 ft (14,000 m), capable of delivering 10,000 lb (4,500 kg) of bombs to targets 5,000 miles (8,000 km) away. At the time, these requirements far exceeded the best technology available.
On 1941 November, the United States Army Air Forces signed a contract for two experimental aircraft under the designation XB-36, based on design studies previously submitted by Consolidated Aircraft Corporation. A few days later, the Engineering Division at Wright Field decided that Consolidated's six-engine design, with all engines on the trailing edge of the wing, was the best option for the aircraft. The original design used vertical stabilizers and rudders, similar to those used in the B-24 Liberator. By the time the first XB-36 was delivered, the design had been changed to a huge single tail, and the wingspan increased to 230 ft (70 m), an unprecedented size.
NB-36H was the one B-36H (serial 51-5712) with a nuclear reactor installed in the rear fuselage for tests.
The first (and only) XB-36 was completed at the Consolidated Fort Worth factory in late 1945. The plane sat on huge wheels 9 ft (2.8 m) in diameter; only three airfields in the USA had concrete thick enough to support the pressure exerted by the original main gear that featured one massive tire and that exerted 156 pounds per square inch.
In 1948 June, the single-wheel undercarriage was replaced by a new undercarriage consisting of two wheels with half the diameter on each strut. This design, which would become the production standard, enabled the B-36 to operate on runways of reasonable thickness.
the SAC wanted to see if the big bomber could operate from rough fields as well. With that the B-36's huge tires gave way to experimental tracked landing gear, to reduce ground pressure for soft-field use.