On August 6, 1945, an American bomber dropped the first deployed atomic bomb on Hiroshima, a city in Japan. The explosion obliterated 90% of the city and killed 80,000 people immediately, with tens of thousands more dying later from radiation exposure. Three days later, another B-29 released a second atomic bomb on Nagasaki, causing approximately 40,000 deaths. These devastating events were made possible by the remarkable Boeing B-29 Superfortress.
During World War II, the United States Army Air Corps determined that the Boeing B-17 Flying Fortress, the primary strategic bomber for the United States during the war, would not suffice for the Pacific Theatre. This area required a bomber capable of carrying a larger payload over distances exceeding 3,000 miles.
In 1938, Boeing initiated the development of pressurized long-range bombers. Their Model 334 design study was a pressurized version of the Boeing B-17 Flying Fortress, featuring a nose-wheel undercarriage. Despite the Air Corps lacking the funds to pursue this design, Boeing continued its development independently. In April 1939, Charles Lindbergh persuaded General Henry H. Arnold to mass-produce a new bomber to counter Nazi production. By December 1939, the Air Corps released a formal specification for a "superbomber" capable of delivering 20,000 lbs of bombs to a target 2,667 miles away at a speed of 400 mph. Boeing's earlier private venture studies served as the foundation for their response to this specification.
On May 11, 1940, Boeing presented its Model 345, competing with designs from Consolidated Aircraft’s Model 33, which later became the B-32, as well as the Lockheed XB-30 and Douglas XB-31. Douglas and Lockheed soon discontinued their projects, but Boeing was awarded an order for two flying prototypes, designated as the XB-29, and an airframe for static testing on August 24, 1940. This order was later amended on December 14 to include a third flying aircraft. Meanwhile, Consolidated continued developing its Model 33, as the Air Corps considered it a backup in case Boeing's design encountered issues.
In May 1941, Boeing received its first production order for 14 service test aircraft and 250 production bombers, which was later increased to 500 aircraft in January 1942. The B-29 had a fuselage with a circular cross-section for enhanced strength, a design first seen in the highly successful Douglas DC3. The requirement for cockpit pressurization also made the B-29 one of the few American combat aircraft during World War II to feature a stepless cockpit design, lacking a separate windscreen for the pilots.
Producing the B-29 was a complicated undertaking. It required four primary assembly factories: two Boeing-operated facilities in Renton, Washington, and Wichita, Kansas; a Bell facility in Marietta, Georgia, near Atlanta; and a Martin facility in Omaha, Nebraska. The project also involved thousands of subcontractors.
The initial prototype took its first flight from Boeing Field in Seattle on September 21, 1942. The aircraft's cutting-edge design, demanding specifications, intense production pressure, and rushed development led to delays. The second prototype, equipped with a Sperry defensive armament system featuring remote-controlled gun turrets sighted by periscopes, unlike the unarmed prototype, made its first flight on December 30, 1942, but this flight was cut short due to a significant engine fire.
On 18 February 1943, the second prototype, departing from Boeing Field in Seattle, suffered an engine fire and crashed. The crash resulted in the deaths of Boeing test pilot Edmund T. Allen, his 10-man crew, 20 workers at the Frye Meat Packing Plant, and a Seattle firefighter. Changes to the production aircraft were so frequent and rapid that by early 1944, B-29s were flown directly from the production lines to modification depots for extensive rebuilds to incorporate the latest updates. AAF-contracted modification centres and its air depot system struggled to manage the extensive requirements. Some facilities lacked hangars large enough to accommodate the massive B-29, necessitating outdoor work in freezing cold weather, which further delayed necessary modifications. By the end of 1943, although nearly 100 aircraft had been delivered, only 15 were airworthy. This led to an intervention by General Hap Arnold to address the issue, with production personnel being dispatched from the factories to the modification centres to expedite the availability of sufficient aircraft to equip the first Bomb Groups in what became known as the "Battle of Kansas." This effort resulted in 150 aircraft being modified in the five weeks between 10 March and 15 April 1944.
The engines were the primary source of maintenance issues and catastrophic failures. While the Wright R-3350 Duplex-Cyclone radial engines eventually became reliable in large piston-engine aircraft, the initial models had severe reliability issues. These were not fully resolved until the aircraft was equipped with the more powerful Pratt & Whitney R-4360 "Wasp Major" in the B-29D/B-50 program, which was introduced too late for World War II. Interim solutions included adding cuffs to the propeller blades to increase cooling airflow into the intakes, which had baffles to direct air onto the exhaust valves. Oil flow to the valves was also increased, asbestos baffles were installed around rubber push rod fittings to prevent oil leaks, thorough pre-flight inspections were conducted to detect unseated valves, and the top five cylinders were replaced every 25 hours of engine time, with complete engine replacements every 75 hours.
Pilots characterize the period immediately after take-off as a critical effort to achieve airspeed, although it should ideally focus on gaining altitude. Radial engines require airflow for cooling, and not reaching adequate speed quickly could lead to engine failure and a potential fire hazard. A helpful method was to test the magnetos while already rolling for take-off, instead of conducting a traditional static engine run-up beforehand.
During wartime, the B-29 could fly at altitudes as high as 31,850 feet and reach speeds of up to 350 mph. This capability served as its primary defence, as Japanese fighters struggled to reach such heights, and even fewer could match the B-29's speed if they did. Only the most powerful anti-aircraft guns could target it, and without proximity fuses, Axis forces found it challenging to hit or damage the aircraft from the ground in combat.
The General Electric Central Fire Control system on the B-29 managed four remote turrets, each equipped with two .50 Browning M2 machine guns. These weapons were aimed using optical sights, with targeting calculated by analogue electrical instruments. Five interconnected sighting stations were positioned in the nose and tail, along with three Plexiglas blisters in the central fuselage. Five General Electric analogue computers, one for each sight, enhanced weapon accuracy by adjusting for airspeed, lead, gravity, temperature, and humidity. These computers also enabled a single gunner to control multiple turrets at once. The gunner in the upper position served as the fire control officer, allocating turret control to other gunners during combat. Initially, the tail position featured two .50 Browning machine guns and a single M2 20 mm cannon. In later models, the 20 mm cannon was removed and sometimes replaced with a third machine gun.
In early 1945, Major General Curtis LeMay, commander of the XXI Bomber Command, ordered the removal of most defensive armament and remote-controlled sighting equipment from the B-29s under his command. This adjustment gave the aircraft the same reduced defensive firepower as the Silverplate B-29 airframes, designed for nuclear weapon delivery, allowing them to carry more fuel and bombs. The reduction in defensive armament was feasible due to a shift in mission strategy from high-altitude, daylight bombing with high explosive bombs to low-altitude night raids using incendiary bombs. As a result, Bell Atlanta produced 311 B-29Bs without turrets and sighting equipment, except for the tail position, which was equipped with AN/APG-15 fire control radar. This version could also be fitted with an improved APQ-7 "Eagle" bombing-through-overcast radar housed in an aerofoil-shaped radome under the fuselage. Most of these aircraft were assigned to the 315th Bomb Wing at Northwest Field, Guam.
For the first time in a bomber, the crew experienced the comfort of full pressurization. This pioneering cabin pressure system for an Allied production bomber was developed by Garrett AiResearch for the B-29. The nose and cockpit were pressurized, but the designers had to decide whether to have non-pressurized bomb bays between the front and rear pressurized sections or a fully pressurized fuselage that required depressurization to drop bombs. The solution was a long tunnel over the two bomb bays, allowing continuous pressurization during the bombing. Crews could move between the front and rear sections through this pressurized tunnel, while the bomb bays remained unpressurized.
Possibly the most renowned B-29s were the sixty-five from the Silverplate series, specifically modified to deliver atomic bombs. These aircraft had all their guns removed, except for the tailguns, to reduce weight. Lieutenant Colonel Paul W. Tibbets personally selected the Silverplate aircraft for the mission directly from the assembly line at the Omaha plant, which later became Offutt Air Force Base. The Silverplate bombers were distinct from other B-29s at the time due to their fuel injection and reversible propellers.
Hiroshima, a manufacturing hub with a population of approximately 350,000, situated around 500 miles from Tokyo, was chosen as the initial target. Upon reaching the U.S. base on Tinian, a Pacific island, the uranium-235 bomb weighing over 9,000 pounds was loaded onto a modified B-29 bomber named "Enola Gay" (after the pilot Colonel Paul Tibbets' mother). The aircraft released the bomb, called "Little Boy," by parachute at 8:15 a.m., and it detonated 2,000 feet above Hiroshima, producing a blast equivalent to 15,000 tons of TNT and devastating five square miles of the city.
The destruction in Hiroshima did not lead to an immediate Japanese surrender. Consequently, on August 9, Major Charles Sweeney piloted another B-29 bomber, "Bockscar," from Tinian. Due to thick clouds over the primary target, Kokura, Sweeney redirected to the secondary target, Nagasaki, where the plutonium bomb "Fat Man" was dropped at 11:02 that morning. This bomb, more powerful than the one used at Hiroshima, weighed nearly 10,000 pounds and was designed to produce a 22-kiloton blast. However, Nagasaki's topography, with its narrow valleys between mountains, mitigated the bomb's impact, confining the destruction to 2.6 square miles.
At noon on August 15, 1945, Japanese time, Emperor Hirohito declared his nation's surrender via a radio broadcast. The announcement rapidly circulated, leading to "Victory in Japan" or "V-J Day" celebrations throughout the United States and other Allied countries. The official surrender document was signed on September 2 on the U.S. battleship Missouri, which was stationed in Tokyo Bay.
After Japan's surrender, B-29s were repurposed for various tasks. Some were used to deliver food and essentials to POWs by dropping barrels of supplies on Japanese POW camps. In September 1945, a long-distance flight was conducted for public relations: Generals Barney M. Giles, Curtis LeMay, and Emmett O'Donnell Jr. flew three specially modified B-29s from Chitose Air Base in Hokkaidō to Chicago Municipal Airport, then continued to Washington, D.C. This was the longest nonstop distance, 6,400 miles, flown by U.S. Army Air Forces aircraft at that time and the first nonstop flight from Japan to Chicago. Two months later, Colonel Clarence S. Irvine led another modified B-29, “Pacusan Dreamboat,” on a world-record long-distance flight from Guam to Washington, D.C., covering 7,916 miles in 35 hours, with a gross take-off weight of 155,000 pounds. Almost a year later, in October 1946, the same B-29 flew 9,422 miles nonstop from Oahu, Hawaii, to Cairo, Egypt, in less than 40 hours, showcasing the potential for airline routes over the polar ice cap.
Comments