|A USAAF B-29 Superfortress|
|Role||Strategic bomber, Heavy bomber|
|First flight||21 September 1942|
|Introduction||8 May 1944|
|Retired||21 June 1960|
|Status||Retired (see Surviving aircraft)|
|Primary users||United States Army Air Forces|
United States Air Force
Royal Air Force
Boeing KB-29 Superfortress
Boeing XB-44 Superfortress
Boeing B-50 Superfortress
|Boeing 377 Stratocruiser|
The Boeing B-29 Superfortress is a four-engine propeller-driven heavy bomber designed by Boeing, which was flown primarily by the United States during World War II and the Korean War. It was one of the largest aircraft operational during World War II and featured state-of-the-art technology. Including design and production, at over $3 billion it was the single most expensive weapons project undertaken by the United States in World War II, exceeding the cost of the Manhattan Project by between $1 and 1.7 billion. Innovations introduced included a pressurized cabin, dual-wheeled, tricycle landing gear, and an analog computer-controlled fire-control system directing four remote machine gun turrets that could be operated by a single gunner and a fire-control officer. A manned tail gun installation was semi-remote. The name "Superfortress" continued the pattern Boeing started with its well-known predecessor, the B-17 Flying Fortress. Designed for the high-altitude strategic bomber role, the B-29 also excelled in low-altitude nighttime incendiary bombing missions. One of the B-29's final roles during World War II was carrying out the atomic bomb attacks on Hiroshima and Nagasaki.
Because of the B-29's advanced design, unlike many other World War II-era bombers, the Superfortress remained in service long after the war ended, with a few even being employed as flying television transmitters for the Stratovision company. The B-29 served in various roles throughout the 1950s. The Royal Air Force flew the B-29 as the Washington until phasing out the type in 1954. The Soviet Union produced an unlicensed reverse-engineered copy as the Tupolev Tu-4. The B-29 was the progenitor of a series of Boeing-built bombers, transports, tankers, reconnaissance aircraft and trainers including the B-50 Superfortress (the first aircraft to fly around the world non-stop) which was essentially a re-engined B-29. The type was retired in the early 1960s. The B-29 production total was 3,970 aircraft. Dozens of B-29s remain as static displays, but only two examples, Fifi and Doc, have been restored to flying status, with Doc flying again for the first time from McConnell AFB on July 17, 2016.
A transport developed from the B-29 was the Boeing C-97 Stratofreighter, first flown in 1944, followed by its commercial airliner variant, the Boeing Model 377 Stratocruiser in 1947. This bomber-to-airliner derivation was similar to the B-17/Model 307 evolution. In 1948 Boeing introduced a tanker variant of the B-29 as the KB-29, followed by the Model 377-derivative KC-97 introduced in 1950. A heavily modified line of outsized-cargo variants of the Stratocruiser is the Guppy / Mini Guppy / Super Guppy, which remain in service today with operators including NASA.
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 (4,292 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. AAF-contracted modification centers and its own air depot system struggled to handle the scope of the requirements. Some facilities lacked hangars capable of housing the giant B-29, requiring outdoor work in freezing cold weather, further delaying necessary modification. By 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 availability 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 five 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).[N 1]
Pilots, including the present day pilots of the Commemorative Air Force's Fifi, one of the last two remaining flying B-29s, 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 General Electric Central Fire Control system on the B-29 directed four remotely controlled turrets armed with two .50 Browning M2 machine guns each.[N 2] 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.[N 3] 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--ordered most of the defensive armament and remote-controlled sighting equipment removed from the B-29s under his command. The affected aircraft had the same reduced defensive firepower as the nuclear weapons-delivery intended Silverplate B-29 airframes, but could carry greater fuel and bomb loads as a result of the change. The lighter defensive armament was made possible by a change in mission 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.[N 4] 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.
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.
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 Yawata, Kyoto Prefecture, 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,[N 5] 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 the 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. [N 6] 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.
In addition to the logistical problems associated with operations from China, the B-29 could only reach a limited part of Japan while flying from Chinese bases. The solution to this problem was to capture the Mariana Islands, which would bring targets such as Tokyo, about 1,500 mi (2,400 km) north of the Marianas within range of B-29 attacks. The Joint Chiefs of Staff agreed in December 1943 to seize the Marianas.
A joint US forces invaded Saipan on 15 June 1944. Despite a Japanese naval counterattack which led to the Battle of the Philippine Sea and heavy fighting on land, Saipan was secured by 9 July. Operations followed against Guam and Tinian, with all three islands secured by August.
Naval construction battalions (Seabees) began at once to construct air bases suitable for the B-29, commencing even before the end of ground fighting. In all, five major air fields were built: two on the flat island of Tinian, one on Saipan, and two on Guam. Each was large enough to eventually accommodate a bomb wing consisting of four bomb groups, giving a total of 180 B-29s per airfield. These bases could be supplied by ship, and unlike the bases in China, were not vulnerable to attacks by Japanese ground forces. The bases became the launch sites for the large B-29 raids against Japan in the final year of the war. The first B-29 arrived on Saipan on 12 October 1944, and the first combat mission was launched from there on 28 October 1944, with 14 B-29s attacking the Truk atoll. The 73rd Bomb Wing launched the first mission against Japan from bases in the Marianas, on 24 November 1944, sending 111 B-29s to attack Tokyo. For this first attack on the Japanese capital since the Doolittle Raid in April 1942, 73rd Bomb Wing wing commander Brigadier General Emmett O'Donnell Jr. acted as mission command pilot in B-29 Dauntless Dotty. The campaign of incendiary raids started with the bombardment of Kobe on February 4, 1945, then peaked early with the most destructive bombing raid in human history (even when the later Silverplate-flown nuclear attacks on Hiroshima and Nagasaki are considered)on the night of March 9-10, 1945 on Tokyo. From then on, the raids intensified, being launched regularly until the end of the war. The attacks succeeded in devastating most large Japanese cities (with the exception of Kyoto and several others), and they gravely damaged Japan's war industries. Although less publicly appreciated, the mining of Japanese ports and shipping routes (Operation Starvation) carried out by B-29s from April 1945 reduced Japan's ability to support its population and move its troops.
Perhaps the most famous B-29s were the sixty-five examples of the Silverplate series, which were modified to drop atomic bombs. They were also stripped of all guns, except the tail ones, in order to have a lighter plane. The Silverplate aircraft were handpicked by Lieutenant Colonel Paul W. Tibbets for the mission, straight off the assembly line at the Omaha plant that was to become Offutt Air Force Base. The Silverplate bombers differed from other B-29s then in service by having fuel injection and reversible props. Pilot Charles Sweeney credits the reversible props for saving Bockscar after making an emergency landing on Okinawa following the Nagasaki bombing.
Enola Gay, flown by Tibbets, dropped the first bomb, called Little Boy, on Hiroshima on 6 August 1945. Enola Gay is fully restored and on display at the Smithsonian's Steven F. Udvar-Hazy Center, outside Dulles Airport in Washington, D.C. Bockscar dropped the second bomb, called Fat Man, on Nagasaki three days later. Bockscar is on display at the National Museum of the United States Air Force.
Following the surrender of Japan, called V-J Day, B-29s were used for other purposes. A number supplied POWs with food and other necessities by dropping barrels of rations on Japanese POW camps. In September 1945, a long-distance flight was undertaken for public relations purposes: Generals Barney M. Giles, Curtis LeMay, and Emmett O'Donnell Jr. piloted three specially modified B-29s from Chitose Air Base in Hokkaid? to Chicago Municipal Airport, continuing to Washington, D.C., the farthest nonstop distance (c.6400 miles) to that date flown by U.S. Army Air Forces aircraft and the first-ever nonstop flight from Japan to the U.S.[N 7] Two months later, Colonel Clarence S. Irvine commanded another modified B-29, Pacusan Dreamboat, in a world-record-breaking long-distance flight from Guam to Washington, D.C., traveling 7,916 miles (12,740 km) in 35 hours, with a gross takeoff weight of 155,000 pounds (70,000 kg). 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, further proving the capability of routing airlines over the polar icecap.
Although considered for other theaters, and briefly evaluated in the United Kingdom, the B-29 was exclusively used in World War II in the Pacific Theatre. The use of YB-29-BW 41-36393, the so-named Hobo Queen, one of the service test aircraft flown around several British airfields in early 1944, was part of a "disinformation" program from its mention in an American-published Sternenbanner German language propaganda leaflet from Leap Year Day in 1944, meant to be circulated within the Reich, with the intent to deceive the Germans into believing that the B-29 would be deployed to Europe.
American post-war military assistance programs loaned the RAF enough Superfortresses to equip several RAF Bomber Command squadrons. The aircraft were known as the Washington B.1 in RAF service, and served from March 1950 until the last bombers were returned in early 1954. The phase out had been occasioned by deliveries of the English Electric Canberra bombers. Three Washingtons modified for ELINT duties and a standard bomber version used for support by No. 192 Squadron RAF were decommissioned in 1958, being replaced by de Havilland Comet aircraft.
Two British Washington B.1 aircraft were transferred to the Royal Australian Air Force (RAAF) in 1952. They were attached to the Aircraft Research and Development Unit and used in trials conducted on behalf of the British Ministry of Supply. Both aircraft were placed in storage in 1956 and were sold for scrap in 1957.
At the end of World War II, Soviet development with modern four-engined heavy bombers lagged behind the west. The Petlyakov Pe-8 -- the sole heavy bomber operated by the VVS--first flew in 1936. Intended to replace the obsolete Tupolev TB-3, only 93 Pe-8s were built by the end of World War II. During 1944 and 1945 five B-29s made emergency landings in Soviet territory after bombing raids on Japanese Manchuria and Japan. In accordance with Soviet neutrality in the Pacific War, the bombers were interned by the Soviets despite American requests for their return. Rather than return the aircraft, the Soviets reverse engineered the American B-29s and used them as a pattern for the Tupolev Tu-4.
On 31 July 1944 Ramp Tramp (serial number 42-6256), of the United States Army Air Force 462nd (Very Heavy) Bomb Group was diverted to Vladivostok, Russia, after an engine failed and the propeller could not be feathered.[N 8] This B-29 was part of a 100-aircraft raid against the Japanese Showa steel mill in Anshan, Manchuria. On 20 August 1944, Cait Paomat (42-93829), flying from Chengdu, was damaged by anti-aircraft gunfire during a raid on the Yawata Iron Works. Due to the damage sustained, the crew elected to divert to the Soviet Union. The aircraft crashed in the foothills of Sikhote-Alin mountain range east of Khabarovsk after the crew bailed out.
On 11 November 1944, during a night raid on Omura on Kyushu Japan, the General H.H. Arnold Special (42-6365) was damaged and forced to divert to Vladivostok in the Soviet Union. The crew was interned. On 21 November 1944, Ding Hao (42-6358) was damaged during a raid on an aircraft factory at Omura, Japan, and was also forced to divert to Vladivostok.
The interned crews of these four B-29s were allowed to escape into American-occupied Iran in January 1945 but none of the B-29s were returned after Stalin ordered the Tupolev OKB to examine and copy the B-29, and produce a design ready for quantity production as soon as possible.[N 9]
Because aluminum in the USSR was supplied in different gauges from that available in the US (metric vs imperial), the entire aircraft had to be extensively re-engineered. In addition, Tupolev substituted his own favored airfoil sections for those used by Boeing, with the Soviets themselves already having their own Wright R-1820-derived 18 cylinder radial engine, the Shvetsov ASh-73 of comparable power and displacement to the B-29's Duplex Cyclone radials available to power their design. In 1947, the Soviets debuted both the Tupolev Tu-4 (NATO ASCC code named Bull), and the Tupolev Tu-70 transport variant. The Soviets used tail-gunner positions similar to the B-29 in many later bombers and transports.[N 10]
Production of the B-29 was phased out after World War II with the last example completed by Boeing's Renton factory on 28 May 1946. Many aircraft went into storage, being declared excess inventory and were ultimately scrapped as surplus. Others remained in the active inventory and equipped the Strategic Air Command when it formed on 21 March 1946. In particular, the "Silverplate" modified aircraft of the 509th Composite Group remained the only aircraft capable of delivering the atomic bomb, and so the unit was involved in the Operation Crossroads series of tests, with B-29 Dave's Dream dropping a "Fat Man"-type bomb in Test Able on 1 July 1946.
Some B-29s, fitted with filtered air sampling scoops, were used to monitor above ground nuclear weapons testing by the United States and the USSR by sampling airborne radioactive contamination. The USAF also used the aircraft for long-range weather reconnaissance (WB-29), for signals intelligence gathering (EB-29) and photographic reconnaissance (RB-29).
The B-29 was used in 1950-53 in the Korean War. At first, the bomber was used in normal strategic day-bombing missions, though North Korea's few strategic targets and industries were quickly reduced to rubble. More importantly, in 1950 numbers of Soviet MiG-15 jet fighters appeared over Korea, and after the loss of 28 aircraft, future B-29 raids were restricted to night-only missions, largely in a supply-interdiction role. Over the course of the war, B-29s flew 20,000 sorties and dropped 200,000 tonnes (180,000 tons) of bombs. B-29 gunners were credited with shooting down 27 enemy aircraft.
The B-29 dropped the 1,000-lb VB-3 "Razon" (a range-controllable version of the earlier Azon guided ordnance device) and the 12,000 lb. VB-13 "Tarzon" MCLOS radio-controlled bombs in Korea, mostly for demolishing major bridges, like the ones across the Yalu River, and for attacks on dams. The aircraft also was used for numerous leaflet drops in North Korea, such as those for Operation Moolah.
A Superfortress of the 91st Strategic Reconnaissance Squadron flew the last B-29 mission of the war on 27 July 1953. Over the three years 16 B-29 and reconnaissance variants were lost to North Korean fighters, four to anti-aircraft fire and 14 to other operational causes.
With the arrival of the mammoth Convair B-36, the B-29 was reclassified as a medium bomber by the Air Force. However, the later B-50 Superfortress variant (initially designated B-29D) was good enough to handle auxiliary roles such as air-sea rescue, electronic intelligence gathering, air-to-air refueling, and weather reconnaissance.
The B-50D was replaced in its primary role during the early 1950s by the Boeing B-47 Stratojet, which in turn was replaced by the Boeing B-52 Stratofortress. The final active-duty KB-50 and WB-50 variants were phased out in the mid-1960s, with the final example retired in 1965. A total of 3,970 B-29s were built.
The variants of the B-29 were outwardly similar in appearance but were in fact built around different wing center sections that affected the wingspan dimensions. The wing of the Renton built B-29A-BN used a different subassembly process and was a foot longer in span. The Georgia built B-29B-BA weighed less through armament reduction. A planned C series with more reliable R-3350s was not built.
Moreover, engine packages changed including the type of propellers and range of the variable pitch. A notable example were the Silverplate project built for the Manhattan Project with Curtiss Electric reversible pitch propellers.
The other differences came about through added equipment for varied mission roles. These roles included cargo carriers (CB); rescue aircraft (SB); weather ships (WB); and trainers (TB); and aerial tankers (KB).
Some were used for odd purposes such as flying relay television transmitters under the name of Stratovision.
The B-29D led progressively to the XB-44, and the family of B-50 Superfortress (which was powered by four 3,500 hp (2,600 kW) Pratt & Whitney R-4360-35 Wasp Major engines).
Another role was as a mothership. This included being rigged for carrying the experimental parasite fighter aircraft, such as the McDonnell XF-85 Goblin and Republic F-84 Thunderjets as in flight lock on and offs. It was also used to develop the Airborne Early Warning program; it was the ancestor of various modern radar picket aircraft. A B-29 with the original Wright Duplex Cyclone powerplants was used to air-launch the famous Bell X-1 supersonic research rocket aircraft, as well as Cherokee rockets for the testing of ejection seats.
Some B-29s were modified to act as test beds for various new systems or special conditions, including fire-control systems, cold-weather operations, and various armament configurations. Several converted B-29s were used to experiment with aerial refueling and re-designated as KB-29s. Perhaps the most important tests were conducted by the XB-29G; it carried prototype jet engines in its bomb bay, and lowered them into the air stream to conduct measurements.
Twenty-two B-29s are preserved at various museums worldwide, including two flying examples; FIFI, which belongs to the Commemorative Air Force, and Doc, which belongs to Doc's Friends. Doc made its first flight in 60 years from Wichita, Kansas, on 17 July 2016. There are also four complete airframes either in storage or under restoration, eight partial airframes in storage or under restoration, and four known wreck sites.
The B-29 Miss Marilyn Gay, which flew 27 successful bombing missions mainly over Japan during the Second World War, and five POW relief missions is displayed at Dobbins Air Reserve Base in Georgia. There is a restored B-29A, Jack's Hack, located as part of the 58th Bomb Wing Memorial the New England Air Museum in Windsor Locks, CT. Three of the Silverplate nuclear weapon delivery B-29s survive: the Enola Gay (nose number 82) the B-29 that dropped the first atomic bomb, was fully restored and placed on display at the Smithsonian's Steven F. Udvar-Hazy Center of the National Air & Space Museum near Washington Dulles International Airport in 2003. Similarly, the weapons delivery aircraft for the Nagasaki raid deploying the Fat Man, the Bockscar (nose number 77) is restored and on display at the National Museum of the United States Air Force at Wright-Patterson AFB in Dayton, Ohio. The third is the 15th Silverplate to be delivered, on the last day of the war in the Pacific. It is on display at the National Museum of Nuclear Science and History in Albuquerque, NM, posing with a replica of the Mark-3 "Fat Man" nuclear bomb.
Only two of the 22 museum aircraft are outside the United States, one is the B-29A It's Hawg Wild in the American Air Museum at the Imperial War Museum Duxford in the United Kingdom, the other at the KAI Aerospace Museum in Sachon, South Korea.
B-29 accidents and incidents include a crash of the plane near Clovis, New Mexico, on Friday evening, 10 November 1944 wherein all 15 members of the crew were killed; the 1948 Waycross B-29 crash, which resulted in the United States v. Reynolds lawsuit regarding State Secrets Privilege; the 1948 Lake Mead Boeing B-29 crash; and, the 1953 "Tip Tow" crash. Another well-known crash took place in 1946 near Clingmans Dome on the border of North Carolina and Tennessee. On 11 April 1950 a B-29 departed Kirtland Air Force Base at 9:38 p.m. and crashed into a mountain on Manzano Base approximately three minutes later, killing the crew. Detonators were installed in the nuclear bomb on the aircraft. The bomb case was demolished and some high-explosive (HE) material burned in the gasoline fire. Other pieces of unburned HE were scattered throughout the wreckage. Four spare detonators in their carrying case were recovered undamaged. There were no contamination or recovery problems. The recovered components were returned to the Atomic Energy Commission. Both the weapon and the capsule of nuclear material were on board the aircraft but the capsule was not inserted for safety reasons. A nuclear detonation was not possible.
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