On September 21, 1942, the first Boeing B-29 Superfortress, the XB-29, took off from Boeing Field in Seattle with Edmund Allen, Boeing's chief of flight test, flying and a crew of ten. The flight lasted 75 minutes. It was 99 feet long with a wingspan of 141 feet, and at 105,000 pounds it was by far the largest aircraft the United States had built.
The aircraft had been designed for a war that had not yet started. The Air Corps had asked in 1939 for a very long-range bomber, on the calculation that Britain might fall and the United States might have to bomb Germany from North America. Boeing's Model 345 won in September 1940. By the time it flew, the requirement had become Pacific rather than Atlantic, and the aircraft's range and ceiling were being aimed at Japan.
Three things were new and all three gave trouble. The Wright R-3350 engines were the most powerful radials in production and were prone to overheating and catching fire, and the B-29 had a magnesium crankcase and an exhaust system that ran close to it. The pressurised cabin, needed for the crew at 30,000 feet, was fed by a system that had to be sealed for the gun turrets to be worked by gunners in shirtsleeves. And the armament was remote: five turrets aimed from three sighting stations by an analogue computer that corrected for range, speed and temperature.
The programme nearly failed. Of the first production aircraft delivered in 1943, most were unserviceable, and the engine fires killed crews in training. Curtis LeMay, who took over the Twentieth Air Force in 1944, stripped the guns and gunners out of his aircraft, loaded them with more bombs and flew them at night from 5,000 feet, because the jet stream over Japan made high-altitude precision bombing miss. The firebombing of Tokyo on March 10, 1945, killed an estimated 100,000 people.
The aircraft also carried the two atomic bombs. The 509th Composite Group was formed for the purpose, with specially modified B-29s, and Enola Gay dropped the first on Hiroshima on August 6, 1945, and Bockscar the second on Nagasaki three days later. The war ended in August. About 3,970 B-29s were built, at a cost of about 3 billion dollars, which was more than the Manhattan Project.