Superfortress Over Japan
Had the war ended on V-E Day there could have remained
doubt as to the decisive effects of strategic bombardment. Postwar study revealed that German production actually increased during 1944, and had the Nazi jet fighter program not foundered, defeat of Hitler might have depended entirely on Allied ground forces.
But war against Japan demonstrated air power’s full weight. Japan, whose armed forces suffered 780,000 combat casualties in the entire war, sustained in nine months 806,000 civilian casualties, including 330,000 dead. All were victims of the Boeing B-29 Superfortress, which had proved itself a weapon of war without equal in the history of mankind. A high price had been paid for Japan’s invasions of China and the attack on America.
The bomber which accomplished this feat, making the Kaiser’s Gothas, Hitler’s Heinkels, Japan’s Mitsubishis, and our own B-17s seem rather primitive, was the first Very Heavy Bomber (VHB) class aircraft. Boeing’s B-29 was based on B-15, B-17 and B-l9 developments, but added a pressurized crew cabin so attacks could be made above the effective reach of anti-aircraft fire. Manual turrets seemed incompatible with pressurization, so a remote-control firing system was provided.
On November 10, 1939, General Arnold asked War Department permission to initiate development of a four-engine bomber of 2,000 mile radius “superior in all respects to the B-17B and the B-24.” Permission was granted, and on January 29, 1940, Request for Data R-40B was issued to leading aircraft builders.
When R-40B, which called for a range of 5,333 miles with a ton of bombs, reached Boeing, the Seattle engineers lead by Ed Wells completed a design already under way. Sent to Wright Field by March 5, 1940, Model 341 offered a 76,000 pound design gross weight, 124 feet 7 inches span, 405-mph speed, a capacity of 4,120 gallons of fuel or five tons of bombs, and six hand-operated .50-caliber guns.
But the Air Corps made even higher demands on April 8, 1940, with Type Specification XC-218-A that, along with leak proof tanks and heavier armament, called for a 5,333 mile range with 2,000-pound bomb load, and a bomb capacity, in lieu of fuel, of eight tons. A 300-mph top speed at 25,000 feet and a 30,000-foot service ceiling was the minimum required. While 450 mph and 40,000 feet were “desired”, they proved beyond the reach of conventional power plants.
Boeing replied on May 11,1940, with Model 345, with a 97,700 pound design gross, 141 feet 2 inch span, 382-mph speed, 5,140 gallon fuel capacity, and ten .50-caliber and one 20-mm. gun in remote-controlled turrets. The four engines would be the new 2,200 hp Wright R-3350-13 Duplex Cyclones also used by Lockheed’s entry, Model 51, in the design competition.
“An evaluation board appraised the designs and rated the four competitors in this order of preference: Boeing, Lockheed, Douglas, Consolidated. Contracts for preliminary engineering data were issued to the firms on June 27 and their planes were designated, respectively, the XB-29, XB-30, XB-31, XB-32.” The Lockheed design was simply an armed version of the future Constellation airliner, while the Douglas XB-31 idea was a 99-ton giant with a 207-foot span and four R-4360 Wasp Majors.
Based on comparison of that engineering data, Boeing won a $3,615,095 contract for two XB-29 prototypes on September 6, 1940. A similar contract went to the XB-32 at the same time, while a third prototype machine was added to each in December.
Even before flight testing began, the pressures of war led the Air Force to program 1,644 production aircraft in a three-billion dollar effort that finally produced 3,957 B-29s from four different factories.
So that the B-17 program would not be obstructed, a new factory was built at Wichita, Kansas, utilizing Midwestern labor reserves. An order for fourteen YB-29s, approved on June 6, 1941, was followed on September 6 by a contract for 250 B-29s, and 500 more were added on January 31, 1942. Later, Bell Aircraft was enlisted to build others at a Marietta, Georgia, facility, the first aircraft plant in the old South. A Renton, Washington, plant built for Boeing flying boats was released by the Navy for B-29A production in exchange for Mitchell medium bombers. Finally, Martin’s Omaha factory then building B-26Cs was also, after a short reservation for 400 stillborn B-33As, assigned to B-29s.
Three XB-29s were built at Seattle, using four Wright R-3350-13 Cyclones, each with double turbosuperchargers and 2,200 hp at 25,000 feet. The first, flown September 21, 1942, by Edmund T. Allen, had three-bladed propellers and four teardrop blisters for the periscopic sights of a Sperry fire-control system. These were replaced in the third prototype by hemispheric blisters for the General Electric fire-control system adopted for production aircraft. Only these prototypes had an astrodome behind the pilot’s cockpit.
Problems with the big new engines were the main threat to B-29 tests; 16 engine changes were made in the XB-29’s first 27 test hours. An engine fire interrupted
the second XB-29’s maiden flight December 30, 1942, and another caused a crash that killed everyone aboard on February 18, 1943. Flight tests were halted and the big gamble of industrial resources on an untested aircraft and power plant was in doubt, but after hasty engine improvements, the third prototype was airborne on June 6.