Boeing B-29 Superfortress

The Boeing B-29 Superfortress was a four-engine propeller powered heavy bomber that was flown by the United States Military in World War II and the Korean War, and by other nations afterwards. The name Superfortress was derived from its well-known predecessor, the B-17 Flying Fortress. 

The B-29 was one of the largest aircraft to see service during World War II. It was one of the most advanced bombers of its time, featuring innovations such as a pressurized cabin, a central fire-control system, and remote-controlled machine gun turrets. Though it was designed as a high-altitude daytime bomber, it actually flew more low-altitude nighttime incendiary bombing missions. It was the primary aircraft in the U.S. firebombing campaign against Japan in the final months of World War II, and B-29s carried the atomic bombs that destroyed Hiroshima and Nagasaki. 

Unlike many most bombers deployed during the Second World War, the B-29 remained in service long after the war ended, with a few even being employed as flying television transmitters for Stratovision. The last operational B-29 heavy bombers were retired in 1960, with 3,960 aircraft having been built between 1943 and 1946.

Boeing B-29 Superfortress
Class Aircraft
Type Bomber
Manufacturer Boeing
Origin United States of America
Country Name Origin Year
United States of America 1942
Country Name Operational Year Retirement Year
United Kingdom - UK (Great Britain) View
United States of America 1944 1960 View
ManufacturerName Production From Production To Quantity
Boeing 3970 View

Boeing began work on pressurized long-range bombers in 1938, in response to a United States Army Air Corps request. Boeing's design study for the Model 334 was a pressurized derivative of the Boeing B-17 Flying Fortress with nosewheel undercarriage. Although the Air Corps did not have money to pursue the design, Boeing continued development with its own funds as a private venture. In April 1939, Charles Lindbergh convinced general Henry H. Arnold to produce a new bomber in large numbers to counter the Nazi production. The Air Corps issued a formal specification for a so-called "superbomber", capable of delivering 20,000 lb (9,100 kg) of bombs to a target 2,667 mi (4,290 km) away and capable of flying at a speed of 400 mph (640 km/h) in December 1939. Boeing's previous private venture studies formed the starting point for its response to this specification.

Boeing submitted its Model 345 on 11 May 1940, in competition with designs from Consolidated Aircraft (the Model 33, later to become the B-32), Lockheed (the Lockheed XB-30), and Douglas (the Douglas XB-31). Douglas and Lockheed soon abandoned work on their projects, but Boeing received an order for two flying prototypes, given the designation XB-29, and an airframe for static testing on 24 August 1940, with the order being revised to add a third flying aircraft on 14 December. Consolidated continued to work on its Model 33 as it was seen by the Air Corps as a backup in case of problems with Boeing's design. Boeing received an initial production order for 14 service test aircraft and 250 production bombers in May 1941, this being increased to 500 aircraft in January 1942. The B-29 featured a fuselage design with circular cross-section for strength. The need for pressurization in the cockpit area also led to the B-29 being one of very few American combat aircraft of World War II to have a stepless cockpit design, without a separate windscreen for the pilots.

Manufacturing the B-29 was a complex task. It involved four main-assembly factories: a pair of Boeing operated plants at Renton, Washington (Boeing Renton), and Wichita, Kansas (now Spirit AeroSystems), a Bell plant at Marietta, Georgia ("Bell-Atlanta"), and a Martin plant at Omaha, Nebraska ("Martin-Omaha" - Offutt Field). Thousands of subcontractors were involved in the project. The first prototype made its maiden flight from Boeing Field, Seattle on 21 September 1942. The combined effects of the aircraft's highly advanced design, challenging requirements, and immense pressure for production, hurried development and caused setbacks. The second prototype, which, unlike the unarmed first, was fitted with a Sperry defensive armament system using remote-controlled gun turrets sighted by periscopes, first flew on 30 December 1942, this flight being terminated due to a serious engine fire. On 18 February 1943, the second prototype, flying out of Boeing Field in Seattle, experienced an engine fire and crashed. The crash killed Boeing test pilot Edmund T. Allen and his 10 man crew, 20 workers at the Frye Meat Packing Plant and a Seattle firefighter. Changes to the production craft came so often and so fast that in early 1944, B-29s flew from the production lines directly to modification depots for extensive rebuilds to incorporate the latest changes. The AAF contracted modification centers and its own air depot system struggled to cope with the scope of the requirement. Some facilities lacked hangars capable of housing the B-29 (which) combined with freezing cold weather further delaying the modifications, such that at the end of 1943, although almost 100 aircraft had been delivered, only 15 were airworthy. This prompted an intervention by General Hap Arnold to resolve the problem, with production personnel being sent from the factories to the modification centers to speed modification of sufficient aircraft to equip the first Bomb Groups in what became known as the "Battle of Kansas". This resulted in 150 aircraft being modified in the six weeks between 10 March and 15 April 1944.

The most common cause of maintenance headaches and catastrophic failures were the engines. Although the Wright R-3350 Duplex-Cyclone radial engines later became a trustworthy workhorse in large piston-engined aircraft, early models were beset with dangerous reliability problems. This problem was not fully cured until the aircraft was fitted with the more powerful Pratt & Whitney R-4360 "Wasp Major" in the B-29D/B-50 program, which arrived too late for World War II. Interim measures included cuffs placed on propeller blades to divert a greater flow of cooling air into the intakes which had baffles installed to direct a stream of air onto the exhaust valves. Oil flow to the valves was also increased, asbestos baffles installed around rubber push rod fittings to prevent oil loss, thorough pre-flight inspections made to detect unseated valves, and frequent replacement of the uppermost five cylinders (every 25 hours of engine time) and the entire engines (every 75 hours).

Pilots, including the present day pilots of the Commemorative Air Force’s Fifi, the last remaining flying B-29, describe flight after takeoff as being an urgent struggle for airspeed (generally, flight after takeoff should consist of striving for altitude). Radial engines need airflow to keep them cool, and failure to get up to speed as soon as possible could result in an engine failure and risk of fire. One useful technique was to check the magnetos while already on takeoff roll rather than during a conventional static engine-runup before takeoff.

In wartime, the B-29 was capable of flight at altitudes up to 31,850 feet (9,710 m), at speeds of up to 350 mph (560 km/h) (true airspeed). This was its best defense, because Japanese fighters could barely reach that altitude, and few could catch the B-29 even if they did attain that altitude. Only the heaviest of anti-aircraft weapons could reach it, and since the Axis forces did not have proximity fuzes, hitting or damaging the aircraft from the ground in combat proved difficult.

The revolutionary General Electric Central Fire Control system on the B-29 directed four remotely controlled turrets armed with two .50 Browning M2 machine guns each. Some turrets were made according to patents from the Tucker Gun Turret. All weapons were aimed optically with targeting computed by analog electrical instrumentation. There were five interconnected sighting stations located in the nose and tail positions and three Plexiglas blisters in the central fuselage. Five General Electric analog computers (one dedicated to each sight) increased the weapons' accuracy by compensating for factors such as airspeed, lead, gravity, temperature and humidity. The computers also allowed a single gunner to operate two or more turrets (including tail guns) simultaneously. The gunner in the upper position acted as fire control officer, managing the distribution of turrets among the other gunners during combat. The tail position initially had two .50 Browning machine guns and a single M2 20 mm cannon. Later aircraft had the 20 mm cannon removed, and sometimes replaced by a third machine gun.

In early 1945, Major General Curtis Lemay, commander of XXI Bomber Command, the Marianas-based B-29-equipped bombing force — that resulted in the affected aircraft having as little defensive firepower as the atomic mission-intended Silverplate B-29 airframes — ordered most of the defensive armament and remote-controlled sighting equipment removed from the B-29s under his command so that they could carry greater fuel and bomb loads as a result of the change of role from high-altitude, daylight bombing with high explosive bombs to low-altitude night raids using incendiary bombs. As a consequence of this requirement, Bell Atlanta (BA) produced a series of 311 B-29Bs that had turrets and sighting equipment omitted, except for the tail position, which was fitted with AN/APG-15 fire control radar. This version could also have an improved APQ-7 "Eagle" bombing-through-overcast radar fitted in an airfoil shaped radome under the fuselage. Most of these aircraft were assigned to the 315th Bomb Wing, Northwest Field, Guam.

The crew enjoyed, for the first time in a bomber, full-pressurization comfort. This first-ever cabin pressure system for an Allied production bomber was developed for the B-29 by Garrett AiResearch. The nose and the cockpit were pressurized, but the designers were faced with deciding whether to have bomb bays that were not pressurized, between fore and aft pressurized sections, or a fully pressurized fuselage with the need to de-pressurize to drop their loads. The solution was a long tunnel over the two bomb bays so as not to interrupt pressurization during bombing. Crews could crawl back and forth between the fore and aft sections, with both areas and the tunnel pressurized. The bomb bays were not pressurized.

World War II

In September 1941, the Army Air Forces plans for war against Germany and Japan proposed basing the B-29 in Egypt for operations against Germany as British airbases were likely to be overcrowded. Air Force planning throughout 1942 and early 1943 continued to have the B-29 deployed initially against Germany, only transferring to the Pacific after the end of the war in Europe. By the end of 1943, however, plans had changed, partly due to production delays, and the B-29 was dedicated to the Pacific Theater. A new plan implemented at the direction of President Franklin D. Roosevelt as a promise to China, called Operation Matterhorn, deployed the B-29 units to attack Japan from four forward bases in southern China, with five main bases in India, and to attack other targets in the region from China and India as needed. The Chengdu region was eventually chosen over the Guilin region to avoid having to raise, equip, and train 50 Chinese divisions to protect the advanced bases from Japanese ground attack. The XX Bomber Command, initially intended to be two combat wings of four groups each, was reduced to a single wing of four groups because of the lack of availability of aircraft, automatically limiting the effectiveness of any attacks from China.

This was an extremely costly scheme, as there was no overland connection available between India and China, and all supplies had to be flown over the Himalayas, either by transport aircraft or by the B-29s themselves, with some aircraft being stripped of armor and guns and used to deliver fuel. B-29s started to arrive in India in early April 1944. The first B-29 flight to airfields in China (over the Himalayas, or "The Hump") took place on 24 April 1944. The first B-29 combat mission was flown on 5 June 1944, with 77 out of 98 B-29s launched from India bombing the railroad shops in Bangkok and elsewhere in Thailand. Five B-29s were lost during the mission, none to hostile fire.

Forward base in China

On 5 June 1944, B-29s raided Bangkok, in what is reported as a test before being deployed against the Japanese home islands. Sources do not report from where they launched, and vary as to the numbers involved—77, 98, and 114 being claimed. Targets were Bangkok's Memorial Bridge and a major power plant. Bombs fell over two kilometres away, damaged no civilian structures, but destroyed some tram lines and destroyed both a Japanese military hospital and the Japanese secret police headquarters. On 15 June 1944, 68 B-29s took off from bases around Chengdu, 47 B-29s bombed the Imperial Iron and Steel Works at Yahata, Japan. This was the first attack on Japanese islands since the Doolittle raid in April 1942. The first B-29 combat losses occurred during this raid, with one B-29 destroyed on the ground by Japanese fighters after an emergency landing in China, one lost to anti-aircraft fire over Yawata, and another, the Stockett's Rocket (after Capt. Marvin M. Stockett, Aircraft Commander) B-29-1-BW 42-6261, disappeared after takeoff from Chakulia, India, over the Himalayas (12 KIA, 11 crew and one passenger) This raid, which did little damage to the target, with only one bomb striking the target factory complex, nearly exhausted fuel stocks at the Chengdu B-29 bases, resulting in a slow-down of operations until the fuel stockpiles could be replenished. Starting in July, the raids against Japan from Chinese airfields continued at relatively low intensity. Japan was bombed on: 7 July 1944 (14 B-29s), 29 July (70+), 10 August (24), 20 August (61), 8 September (90), 26 September (83), 25 October (59), 12 November (29), 21 November (61), 19 December (36) and for the last time on 6 January 1945 (49).

The tactic of using aircraft to ram American B-29s was first recorded on raid of 20 August 1944 on the steel factories at Yawata. Sergeant Shigeo Nobe of the 4th Sentai intentionally flew his Kawasaki Ki-45 into a B-29; debris from the explosion following this attack severely damaged another B-29, which also went down. Lost were Colonel Robert Clinksale's B-29-10-BW 42-6334 Gertrude C and Captain Ornell Stauffer's B-29-15-BW 42-6368 Calamity Sue, both from the 486th BG. Several B-29s were destroyed in this way over the ensuing months. Although the term "Kamikaze" is often used to refer to the pilots conducting these attacks, the word was not used by the Japanese military.

B-29s were withdrawn from airfields in China by the end of January 1945. Throughout this prior period, B-29 raids were also launched from China and India against many other targets throughout Southeast Asia, including a series of raids on Singapore and Thailand. On 2 November 1944, 55 B-29s raided Bangkok's Bang Sue marshalling yards in the largest raid of the war. Seven RTAF Nakajima Ki-43 Hayabusas from Foong Bin (Air Group) 16 and 14 IJAAF Ki-43s attempted intercept. RTAF Flt Lt Therdsak Worrasap attacked a B-29, damaging it, but was shot down by return fire. One B-29 was lost, possibly the one damaged by Flt Lt Therdsak.  On 14 April 1945, a second B-29 raid on Bangkok destroyed two key power plants, and was the last major attack conducted against Thai targets. The B-29 effort was gradually shifted to the new bases in the Mariana Islands in the Central Pacific, with the last B-29 combat mission from India flown on 29 March 1945.

General characteristics

  • Crew: 11: (A/C)Airplane Commander, Pilot, flight engineer (a rated pilot),. bombardier, navigator, radio operator, radar operator, blister gunners (two), CFC upper gunner, and tail gunner
  • Length: 99 ft 0 in (30.2 m)
  • Wingspan: 141 ft 3 in (43.1 m)
  • Height: 29 ft 7 in (8.5 m)
  • Wing area: 1,736 ft (161.3 m)
  • Empty weight: 74,500 lb (33,800 kg)
  • Loaded weight: 120,000 lb (54,000 kg)
  • Max takeoff weight: 133,500 lb (60,560 kg)
  • Powerplant: 4 x Wright R-3350-23 and 23A turbosupercharged radial engines, 2,200 hp (1,640 kW) each
  • Zero-lift drag coefficient: 0.0241
  • Drag area: 41.16 ft (3.82 m)
  • Aspect ratio: 11.50

Performance

  • Maximum speed: 357 mph (310 knots, 574 km/h)
  • Cruise speed: 220 mph (190 knots, 350 km/h)
  • Stall speed: 105 mph (91 knots, 170 km/h)
  • Combat range: 3,250 mi (2,820 nm, 5,230 km)
  • Ferry range: 5,600 mi (4,900 nm, 9,000 km)
  • Service ceiling 33,600 ft (10,200 m)
  • Rate of climb: 900 ft/min (4.6 m/s)
  • Wing loading: 69.12 lb/ft (337 kg/m)
  • Power/mass: 0.073 hp/lb (121 W/kg)
  • Lift-to-drag ratio: 16.8

Armament

  • Guns:
    • 8 to 10 x .50 in (12.7 mm) caliber Browning M2/ANs in remote controlled turrets
    • 2 x .50 in and 1 x 20 mm M2 cannon in tail position (the cannon was eventually removed as it proved unreliable in service )
    • B-29B-BW - All armament and sighting equipment removed except for tail position; initially 2 x .50 in M2/AN and 1 x 20 mm M2 cannon, later 3 x 2 x .50 in M2/AN with APG-15 gun-laying radar fitted as standard.
  • Bombs: 20,000 lb (9,000 kg) standard loadout, could be modified to externally carry two 22,000 lb (10,000 kg) T-14 Earthquake bombs.

End notes