Among the most sophisticated aircraft flown during World War II, the Boeing B-29 Superfortress was designed to replace the B-17 as the primary long-range bomber of the U.S. Army Air Forces. With its distinctive glazed nose and long, thin wings that provided both speed at high altitude and stability at takeoff and landing, the Superfortress was the first operational bomber with a pressurized crew cabin and featured advanced radar and avionics. Armed with remote-controlled machine gun turrets and a 20,000 pound bomb load, it was the first USAAF bomber capable of mastering the vast distances of the Pacific Theater of World War II. The prototype flew in September 1942 but a series of post-production modifications delayed the bomber's first mission until April 1944. Superfortresses began attacking Japan in daylight with conventional ordnance from high altitude, but their mission was redirected in March 1945, with massive low-level formations dropping incendiary bombs! at night on Japanese cities. The ensuing firestorms, followed by the complete destruction of Hiroshima and Nagasaki by atomic bombs dropped from two specially modified silverplate" B-29s