Boeing B - 29 Superfortress variants The Boeing B - 29 Superfortress was produced in a large number of experiment al and production models . XB - 29 . The XB - 29 , Boeing Model 345 , was the first accepted prototype or experimental model delivered to the Army Air Corps , incorporating a number of improvements on the design originally submitted , including more and larger guns and self - sealing fuel tank s . Two aircraft were ordered in 1940 August , and a third was ordered in December . A mock - up was completed in the spring of 1941 , and it first flew on September 21 , 1942 . Testing continued until February 18 , 1943 , when the second prototype crashed . Flown by Boeing ' s chief test pilot , Edmund T . " Eddie " Allen on a two - hour powerplant performance test , leaking fuel from a filler cap in the leading edge ran down inside the leading - edge and ignited spreading to the engines , due to the much reduced power the aircraft , unable to climb , crashed into the Frye meat - packing plant , demolishing the majority of the packing plant and killing all eleven crew , 22 employees at the plant and one fireman . The crash killed many élite Boeing personnel involved in the design ; the pilot , Allen , was chief of the Research Division . After the crash , the United States Army Air Forces and a congressional committee headed by then - Senator Harry S . Truman investigated the B - 29 program issuing a scathing report , prompting the Army Air Force to take over the program . YB - 29 . The YB - 29 was an improved XB - 29 and 14 were built for service testing . Testing began in the summer of 1943 , and dozens of modifications were made to the planes . The engines were upgraded from Wright R - 3350 - 13s to R - 3350 - 21s . Where the XB - 29 had three - bladed props , the YB - 29 had four - bladed . Various alternatives to the remote - sighted defensive systems were tested on a number of them , particularly the fourth one delivered . After alternative arrangements had been fully tested , defensive armament was standardised at ten . 50 - calibre machine guns in turret - mounted pairs . The YB - 29 also featured a better fire control system . B - 29 . The B - 29 was the original production version of the Superfortress . Since the new bomber was urgently needed , the production design was developed in tandem with the service testing . In fact , the first B - 29 was completed only two months after the delivery of the first YB - 29 . 46 B - 29s of this variant built by the Glenn L . Martin Company at its Omaha plant were used as the aircraft for the atomic bomb missions , modified to Silverplate specifications . 2 , 513 B - 29s were manufactured by Boeing - Wichita ( 1 , 620 ) , Bell - Atlanta ( 357 ) , and Martin - Omaha ( 536 ) . B - 29A . The B - 29A was an improved version of the original B - 29 production model . All 1 , 119 B - 29A ' s were built exclusively at the Boeing plant in Renton , Washington , formerly used by the United States Navy . Enhancements made in the B - 29A included a better wing design and defensive modifications . Due to a demonstrated weakness to head - on fighter attacks , the number of machine guns in the forward dorsal turrets was doubled to four . Where the wings of previous models had been made by the sub - assembly of two sections , the B - 29A began the trend of using three . This made construction easier , and increased the strength of the airframe . The B - 29A was produced until May 1946 , when the last aircraft was completed . It was much used during the Korean War , but was quickly phased out when the jet bomber became operational . Washington B Mk 1 - This was the service name given to 88 B - 29As supplied to the Royal Air Force . B - 29B . The B - 29B was a modification used for low - level raids , designed with the intent of firebombing Japan . Since fighter opposition was minimal over Japan in late 1944 , many of the Army Air Force leadership — most notably Curtis LeMay , commander of the XXI Bomber Command — felt that a ( lighter ) faster bomber would better evade Japanese flak . In the B - 29B , all defensive armament was removed except for that in the tail turret . Initially the armament was two . 50 in M2 / AN machine guns and one 20 mm M2 cannon which was soon changed to three . 50 in M2 / ANs . The weight saved by removing the gun system increased the top speed from 357 mph to 364 mph ( 574 km / h to 586 km / h ) . Also incorporated on this version was an improved APQ - 7 " Eagle " bombing - through - overcast radar fitted in an airfoil shaped radome under the fuselage . All 311 B - 29Bs were built at the Bell plant in Marietta , Georgia ( " Bell - Atlanta " ) . B - 29C . The B - 29C was a modification of the B - 29A re - engined with improved Wright R - 3350 engines . The Army Air Force originally ordered 5 , 000 , but cancelled its request when World War II ended and none were built . B - 29D ( XB - 44 ) . The B - 29D was an improved version of the original B - 29 design , featuring Pratt & Whitney R - 4360 - 35 engines of 3500 hp ( 2600 kW ) each — nearly 60 % more powerful than the Wright R - 3350 . It also had a taller vertical stabiliser and a strengthened wing . The XB - 44 was the testbed designation for the D model . When World War II ended , drastic cutbacks were made in military spending , altering the outlook of the B - 29 program . Because Congress was reluctant to continue funding wartime projects , the B - 29D was redesignated B - 50 to make it appear completely new . Congress fell for the trick , and the B - 29D was kept alive , even though no planes flew under the original designation . Test beds . A number of B - 29s were converted to serve as test beds for new systems . These all received variant designation , even though many existed only as a single converted aircraft . XB - 29E . The XB - 29E for fire - control system s ( one converted ) was a model B - 29 - 45 - BW . XB - 29F . The B - 29F for cold - weather operation in Alaska were six converted B - 29 - BWs . XB - 29G . It was also used in the development of jet engines . Stripped of armament , a converted B - 29B - 55 - BA ( 44 - 84043 ) ( Bell ) designated the XB - 29G carried experimental jet engines in its bomb bay , which it would extend into the airstream for testing during flight . This plane was used to test the Allison J35 , General Electric J47 and J73 jet engines . XB - 29H . The XB - 29H to test armament configurations was a converted B - 29A . YB - 29J , YKB - 29J , RB - 29J . Experimentation in engines continued . For example , six B - 29s ( redesignated YB - 29J ) of various designation were upgraded to R - 3350 - 79 engines . Other engine - associated items were also upgraded , including new Curtiss propellers , and ' Andy Gump ' cowlings , in which the oil coolers have separate air intakes . Two were later converted to aerial refueling tanker prototypes , and redesignated YKB - 29J . The remainder were used for reconnaissance , and designated RB - 29J . " EB - 29 . The EB - 29 ( E stands for exempt ) , was used as a carrier aircraft in which the bomb bay was modified to accept and launch experimental aircraft . They were converted in the years following World War II . One EB - 29 was converted to carry the famous Bell X - 1 until it was replaced by a B - 50 . Another was used to carry and test the XF - 85 ' parasite fighter ' . This fighter was intended to be carried by the Convair B - 36 on long - range missions to protect it from Soviet fighters . Yet another EB - 29 was used to carry two EF - 84B Thunderjet fighters as part of Project Tom - Tom . All three Tom - Tom aircraft and their crews were lost in a crash on April 24 , 1953 . RB - 29J ( RB - 29 , FB - 29J , F - 13 , F - 13A ) . Early B - 29 / B - 29As that were modified for photo reconnaissance carried the F - 13 / F - 13A designations , with " F " meaning ' photo ' . The aircraft ( 118 modified B - 29BWs and B - 29As ) carried three K - 17B , two K - 22 and one K - 18 cameras . Between the end of the war and 1948 the designation was changed to FB - 29J . In 1948 , the F - 13 / FB - 29s were redesignated RB - 29 and RB - 29A . Six B - 29A / F - 13As were modified with the Wright 3350 - CA - 2 fuel injected engines and designated at YB - 29Js . These were then converted to RB - 29Js . In January 1949 , RB - 29s were assigned to the 91st Strategic Reconnaissance Wing and moved to Yokota AB , Japan in December 1950 ; to provide support to the Korean War and attached to the 15th Air Force , Far East Air Force . SB - 29 . The SB - 29 ' Super Dumbo ' was a version of the B - 29 adapted for air - sea rescue duty near the end of World War II . Sixteen 29s were modified to carry a droppable A - 3 lifeboat under the fuselage , the SB - 29 was used mainly as rescue support for air units that flew long distances over water . With the exception of the forward lower gun turret , all defensive armament was retained . They also carried a variety of radio equipment , provisions , survival kits , and extra crew . It was used throughout the Korean War into the mid - 1950s . It received its nickname from " Dumbo " , the Disney character , whose name was given to the aircraft used in previous missions to pick airmen up when they crashed at sea . TB - 29 . The TB - 29 was a trainer conversion of B - 29 used to train crew for bombing missions ; some were also used to tow targets , and the designation included B - 29s modified solely for that purpose . Their most important role was serving as radar targets in the 1950s when the United States Air Force was developing intercept tactics for its fighters . WB - 29 . The WB - 29s were production aircraft modified to perform weather monitoring missions . An observation position was fitted above the central fuselage section . They conducted standard data - gathering flights , including from the UK over the Atlantic , but were also ordered to fly into the eye of a hurricane or typhoon to gather information . Following nuclear weapons tests , some WB - 29s would use air sampling scoops to test radiation levels . On 3 September 1949 , a WB - 29 returning from Yokota AB , Japan , to Eielson AFB , Alaska , recovered radioactive debris in air sampling scoops from the cloud generated by the first atomic bomb test by the Soviet Union on 29 August . Airborne Early Warning . In the middle of 1951 , three B - 29s were modified to participate in the Airborne Early Warning programme . The upper section of the forward fuselage was extensively modified to house an AN / APS - 20C search radar , and the interior was modified to house radar and Electronic Counter Measures ( ECM ) equipment . This development led to production radar picket aircraft , including the EC - 121 Warning Star . ( ×3 , converted ) A Soviet - built copy of B - 29 , Tu - 4 , was used as the platform for a Chinese experimental airborne early warning aircraft , KJ - 1 AEWC , in 1970s . Navy P2B patrol bomber . The U . S . Navy acquired four B - 29 - BWs from the U . S . Army Air Forces on March 14 , 1947 . These aircraft were modified for long - range patrol missions and given the designation P2B - 1S with Navy Bureau Number s ( BuNo ) 84028 , 84029 , 84030 and 84031 . BuNo 84029 , previously AAF Ser . No . 45 - 21787 , later went through modifications to carry the Navy ' s Douglas D - 558 - 2 Skyrocket high - speed rocket - powered research aircraft . Modifications of the bomb bay were done to carry the Skyrocket II under the belly and dropped for Mach speed testing . The first Skyrocket test flight occurred on September 8 , 1950 with test pilot William B . Bridgeman , and George Jansen flying the B - 29 . Scott Crossfield later broke Mach 2 with the Skyrocket on November 20 , 1953 ; with the last Skyrocket flight in December 1956 . The P2B - 1S " mother - ship " was nicknamed " Fertile Myrtle " and was assigned the NACA number 137 . As of May 2013 , this aircraft was in the collection of Kermit Weeks at his Fantasy of Flight aviation museum in Polk City , Florida . The forward fuselage section was restored and briefly displayed at the Florida Air Museum in Lakeland , Florida . It has since been relocated to Fantasy of Flight ' s " Golden Hill " storage facility along with the remainder of the disassembled aircraft and is awaiting full restoration to airworthy flying status at a future date . BuNo 84030 and 84031 were later modified into anti - submarine patrol bombers and redesignated P2B - 2S . XB - 39 Superfortress . The XB - 39 Superfortress was a single YB - 29 modified to use water - cooled Allison V - 3420 - 17 inline engines . Since the Army Air Force was concerned that problems might develop with their first choice of engine , the Wright R - 3350 , they contracted General Motors to do testing on a modified aircraft to show that it could still be used even if the R - 3350 failed . Since the R - 3350 did not have significant enough problems to prevent its use , no XB - 39s were ordered . Tupolev Tu - 4 . In 1945 , three B - 29s were forced to land in Soviet territory after a bombing raid on Japan because of a lack of fuel . Since the Soviet Union was not at war with Japan at the time , the aircraft and crews were interned . Eventually , the B - 29 crew members were returned , but the aircraft remained in Russian hands . Seeking a modern long - range bomber , Joseph Stalin ordered the Tupolev OKB to reverse - engineer the Superfortress . The resulting aircraft first flew on May 19 , 1947 and immediately began series production . Although largely identical in appearance to American B - 29 ' s the Tu - 4 ( Nato reporting name : " Bull " ) , had Soviet - designed defensive guns and had been re - engineered to suit production using metric tools ; resulting in an aircraft that was slightly heavier and slower than the B - 29 . The Tu - 4 presented a significant leap forward in Soviet strategic bombing . Not only did the Red Air Force have the means to deliver nuclear weapons , but Tu - 4 had sufficient range to reach the United States on a one - way trip . On October 18 , 1949 , a Tu - 4 was used in the first air - drop test of a Soviet atomic bomb . In Soviet service , the Tu - 4 had been phased out of service by the early 1960s , being replaced by more modern aircraft such as the Tupolev Tu - 95 . Although the " Bull " never dropped a bomb in anger , the Tu - 4 influenced Soviet aircraft technology , particularly airframe construction and onboard systems . The People ' s Liberation Army Air Force of China is rumoured to still operate up to 15 upgraded Tu - 4s , possibly as AWACS platforms . Advanced transport and bomber variants of the Tu - 4 design such as the Tu - 70 , 75 , 80 , and 85 , were developed and built , but none of these achieved serial production .