Convair B-36 Peacemaker
The Convair B-36 "Peacemaker" is a strategic bomber built by Convair and operated by the United States Air Force (USAF) from 1949 to 1959. The B-36 is the largest mass-produced piston-engined aircraft ever built. It had the longest wingspan of any combat aircraft ever built, at . The B-36 was the first bomber capable of delivering any of the nuclear weapons in the U.S. arsenal from inside its four bomb bays without aircraft modifications. With a range of and a maximum payload of , the B-36 was capable of intercontinental flight without refuelling. Entering service in 1948 , the B-36 was the primary nuclear weapons delivery vehicle of Strategic Air Command (SAC) until it was replaced by the jet-powered Boeing B-52 Stratofortress beginning in 1955. All but four aircraft have been scrapped. Development. The genesis of the B-36 can be traced to early 1941, prior to the entry of the United States into World War II. At the time, the threat existed that Britain might fall to the German "Blitz", making a strategic bombing effort by the United States Army Air Corps (USAAC) against Germany impossible with the aircraft of the time. The United States would need  a new class of bomber that would reach Europe and return to bases in North America, necessitating a combat range of at least , the length of a Gander, Newfoundland–Berlin round trip. The USAAC therefore sought a bomber of truly intercontinental range, similar to the German Reichsluftfahrtministerium's (RLM) ultralong-range "Amerikabomber" program, the subject of a 33-page proposal submitted to Reichsmarschall Hermann Goering on 12 May 1942. The USAAC sent out the initial request on 11 April 1941, asking for a top speed, a cruising speed, a service ceiling of —beyond the range of ground-based anti-aircraft  fire—and a maximum range of at . These requirements proved too demanding for any short-term design, far exceeding the technology of the day, so on 19 August 1941, they were reduced to a maximum range of , an effective combat radius of with a bombload, a cruising speed between , and a service ceiling of —above the maximum effective altitude of Nazi Germany's anti-aircraft guns, save for the rarely deployed 12.8 cm FlaK 40 heavy flak cannon. World War II and after. As the Pacific war progressed, the USAAF increasingly needed a bomber capable of reaching Japan from its  bases in Hawaii, and the development of the B-36 resumed in earnest. Secretary of War Henry L. Stimson, in discussions with high-ranking officers of the USAAF, decided to waive normal army procurement procedures, and on 23 July 1943 – some 15 months after the Germans' "Amerikabomber" proposal's submission made it to their RLM authority, and coincidentally, the same day that, in Germany, the RLM had ordered the Heinkel firm to design a six-engined version of their own, BMW 801E powered "Amerikabomber" design proposal – the USAAF submitted a "letter of intent" to Convair, ordering an initial production run of  100 B-36s before the completion and testing of the two prototypes. The first delivery was due in August 1945, and the last in October 1946, but Consolidated (by this time renamed Convair after its 1943 merger with Vultee Aircraft) delayed delivery. The aircraft was unveiled on 20 August 1945 (three months after V-E Day), and flew for the first time on 8 August 1946. After the establishment of an independent United States Air Force in 1947, the beginning in earnest of the Cold War with the 1948 Berlin Airlift, and the 1949 atmospheric test of the first Soviet atomic  bomb, American military planners sought bombers capable of delivering the very large and heavy first-generation atomic bombs. The B-36 was the only American aircraft with the range and payload to carry such bombs from airfields on American soil to targets in the USSR. The modification to allow the use of larger atomic weapons on the B-36 was called the "Grand Slam Installation". The B-36 was arguably obsolete from the outset, being piston-powered, coupled with the widespread introduction of first-generation jet fighters in potential enemy air forces. However, its jet rival, the Boeing B-47 Stratojet, which did not  become fully operational until 1953, lacked the range to attack the Soviet homeland from North America without aerial refueling and could not carry the huge first-generation Mark 16 hydrogen bomb. The other American piston bombers of the day, the B-29 and B-50, were also too limited in range to be part of America's developing nuclear arsenal. Intercontinental ballistic missiles did not become sufficiently reliable until the early 1960s. Until the Boeing B-52 Stratofortress became operational in 1955, the B-36, as the only truly intercontinental bomber, continued to be the primary nuclear weapons delivery vehicle of the SAC. Convair  touted the B-36 as the "aluminum overcast", a so-called "long rifle" giving SAC truly global reach. During General Curtis LeMay's tenure as head of SAC (1949–57), the B-36, through intense crew training and development, formed the heart of the Strategic Air Command. Its maximum payload was more than four times that of the B-29, and exceeded that of the B-52. The B-36 was slow and could not refuel in midair, but could fly missions to targets away and stay aloft as long as 40 hours. Moreover, the B-36 was believed to have "an ace up its sleeve": a  phenomenal cruising altitude for a piston-driven aircraft, made possible by its huge wing area and six 28-cylinder engines, putting it out of range of most of the interceptors of the day, as well as ground-based anti-aircraft guns. Experimentals and prototypes. Consolidated Vultee Aircraft Corporation (later Convair) and Boeing Aircraft Company took part in the competition, with Consolidated winning a tender on 16 October 1941. Consolidated asked for a $15 million contract with $800,000 for research and development, mockup, and tooling. Two experimental bombers were proposed, the first to be delivered in 30 months, and  the second within another six months. Originally designated Model B-35, the name was changed to B-36 to avoid confusion with the Northrop YB-35 piston-engined flying-wing bomber, against which the B-36 was meant to compete for a production contract. Throughout its development, the B-36 encountered delays. When the United States entered World War II, Consolidated was ordered to slow B-36 development and greatly increase Consolidated B-24 Liberator production. The first mockup was inspected on 20 July 1942, following six months of refinements. A month after the inspection, the project was moved from San Diego, California, to Fort Worth, Texas , which set back development several months. Consolidated changed the tail from a twin-tail to a single, thereby saving , but this change delayed delivery by 120 days. The tricycle landing gear system's initial main gear design, with huge single wheels found to cause significant ground pressure problems, limited the B-36 to operating from just three air bases in the United States: Carswell Field (former Carswell AFB, now NAS JRB Fort Worth/Carswell Field), adjacent to the Consolidated factory in Fort Worth, Texas; Eglin Field (now Eglin AFB), Florida; and Fairfield-Suisun Field (now Travis AFB) in California. As a  result, the Air Force mandated that Consolidated design a four-wheeled bogie-type wheel system for each main gear unit instead, which distributed the pressure more evenly and reduced weight by . Changes in the USAAF requirements did add back any weight saved in redesigns, and cost more time. A new antenna system needed to be designed to accommodate an ordered radio and radar system. The Pratt and Whitney engines were redesigned, adding another . Design. The B-36 took shape as an aircraft of immense proportions. It was two-thirds longer than the previous "superbomber", the B-29. The wingspan and tail height  of the B-36 exceeded those of the 1960s Soviet Union's Antonov An-22 "Antheus" military transport, the largest ever propeller-driven aircraft put into production. Only with the advent of the Boeing 747 and the Lockheed C-5 Galaxy, both designed two decades later, did American aircraft capable of lifting a heavier payload become commonplace. The wings of the B-36 were large even when compared with present-day aircraft, exceeding, for example, those of the C-5 Galaxy, and enabled the B-36 to carry enough fuel to fly the intended long missions without refueling. The maximum thickness of the wing, measured perpendicular  to the chord, was , containing a crawlspace that allowed access to the engines. The wing area permitted cruising altitudes well above the operating ceiling of any 1940s-era operational piston and jet-turbine fighters. Most versions of the B-36 could cruise at over . B-36 mission logs commonly recorded mock attacks against U.S. cities while flying at . In 1954, the turrets and other nonessential equipment were removed (not entirely unlike the earlier Silverplate program for the atomic bomb-carrying "specialist" B-29s) that resulted in a "featherweight" configuration believed to have resulted in a top speed of , and cruise at and dash  at over , perhaps even higher. The large wing area and the option of starting the four jet engines supplementing the piston engines in later versions gave the B-36 a wide margin between stall speed ("V") and maximum speed ("V") at these altitudes. This made the B-36 more maneuverable at high altitude than the USAF jet interceptors of the day, which either could not fly above , or if they did, were likely to stall out when trying to maneuver or fire their guns. However, the U.S. Navy argued that their McDonnell F2H Banshee fighter could intercept the B-36, thanks to its  ability to operate at more than . The USAF declined the invitation from the U.S. Navy for a fly-off between the Banshee and the B-36. Later, the new Secretary of Defense, Louis A. Johnson, who considered the U.S. Navy and naval aviation essentially obsolete in favor of the USAF and SAC, forbade putting the Navy's claim to the test. The propulsion system of the B-36 was unique, with six 28-cylinder Pratt & Whitney R-4360 'Wasp Major' radial engines mounted in an unusual pusher configuration, rather than the conventional four-engine, tractor propeller layout of other heavy bombers. The prototype  R-4360s delivered a total of . While early B-36s required long takeoff runs, this situation was improved with later versions, delivering a significantly increased power output of total. Each engine drove a three-bladed propeller, in diameter, mounted in the pusher configuration, thought to be the second-largest diameter propeller design ever used to power a piston-engined aircraft (after that of the Linke-Hofmann R.II). This unusual configuration prevented propeller turbulence from interfering with airflow over the wing, but could also lead to engine overheating due to insufficient airflow around the engines, resulting in inflight engine fires. The large, slow -turning propellers interacted with the high-pressure airflow behind the wings to produce an easily recognizable very-low-frequency pulse at ground level that betrayed approaching flights. Addition of jet propulsion. Beginning with the B-36D, Convair added a pair of General Electric J47-19 jet engines suspended near the end of each wing; these were also retrofitted to all extant B-36Bs. Consequently, the B-36 was configured to have 10 engines, six radial propeller engines and four jet engines, leading to the B-36 slogan of "six turnin' and four burnin' ". The B-36 had more engines than any other mass-produced aircraft . The jet pods greatly improved takeoff performance and dash speed over the target. In normal cruising flight, the jet engines were shut down to conserve fuel. When the jet engines were shut down, louvers closed off the front of the pods to reduce drag and to prevent ingestion of sand and dirt. The jet engine louvers were opened and closed by the flight crew in the cockpit, whether the B-36 was on the ground or in the air. The two pods with four turbojets and the six piston engines combined gave the B-36 a total of for short periods of  time. Crew. The B-36 had a crew of 15. As in the B-29 and B-50, the pressurized flight deck and crew compartment were linked to the rear compartment by a pressurized tunnel through the bomb bay. In the B-36, movement through the tunnel was on a wheeled trolley, pulling on a rope. The rear compartment featured six bunks and a dining galley, and led to the tail turret. Landing gear. The XB-36 featured a single-wheel main landing gear whose tires were the largest ever manufactured up to that time, tall, wide, and weighing , with enough rubber for 60 automobile  tires. These tires placed so much pressure on runways that the XB-36 was restricted to the Fort Worth airfield adjacent to the plant of manufacture, and to a mere two USAF bases beyond that. At the suggestion of General Henry H. Arnold, the single-wheel gear was soon replaced by a four-wheel bogie. At one point, a tank-like tracked landing gear was also tried on the XB-36, but it proved heavy and noisy. The tracked landing gear was quickly abandoned. Weaponry. The four bomb bays could carry up to of bombs, more than 10 times the load carried  by the World War II workhorse, the Boeing B-17 Flying Fortress, and substantially more than the entire B-17's gross weight. The B-36 was not designed with nuclear weaponry in mind, because the mere existence of such weapons was top secret during the period when the B-36 was conceived and designed (1941–46). Nevertheless, the B-36 stepped into its nuclear delivery role immediately upon becoming operational. In all respects except speed, the B-36 could match what was arguably its approximate Soviet counterpart, the turboprop-powered Tu-95, which began production in January 1956 and was still in active service . Until the B-52  became operational, the B-36 was the only means of delivering the first generation Mark-17 hydrogen bomb, long, in diameter, and weighing , the heaviest and bulkiest American aerial nuclear bomb ever. Carrying this massive weapon required merging two adjacent bomb bays. The defensive armament consisted of six remote-controlled retractable gun turrets, and fixed tail and nose turrets. Each turret was fitted with two 20 mm cannon, for a total of 16. Recoil vibration from gunnery practice often caused the aircraft's electrical wiring to jar loose or the vacuum tube electronics to malfunction, leading to failure of the aircraft controls  and navigation equipment; this contributed to the crash of B-36B 44-92035 on 22 November 1950. The Convair B-36 was the only aircraft designed to carry the T-12 Cloudmaker, a gravity bomb weighing and designed to produce an earthquake bomb effect. Part of the testing process involved dropping two of the bombs on a single flight mission, one from and the second from , for a total bomb load of . The first prototype XB-36 flew on 8 August 1946. The speed and range of the prototype failed to meet the standards set out by the USAAC in 1941. This was expected , as the Pratt & Whitney R-4360 engines required were not yet available, and the qualified workers and materials needed to install them were lacking. A second aircraft, the YB-36, flew on 4 December 1947. It had a redesigned, high-visibility, yet still "greenhouse-like" bubble canopy, heavily framed due to its substantial size, which was later adopted for production, and the engines used on the YB-36 were more powerful and more efficient. Altogether, the YB-36 was much closer to the production aircraft. The first few of 21 B-36As were delivered in 1948. They were interim airframes, intended for crew training and  later conversion. No defensive armament was fitted, since none was ready. Once later models were available, all B-36As were converted to RB-36E reconnaissance models. The first B-36 variant meant for normal operation was the B-36B, delivered beginning in November 1948. This aircraft met all the 1941 requirements, but had serious problems with engine reliability and maintenance (changing the 336 spark plugs was a task dreaded by ground crews) and with the availability of armaments and spare parts. Later models featured more powerful variants of the R-4360 engine, improved radar, and redesigned crew compartments. The four jet engines increased fuel consumption  and reduced range. Gun turrets were already recognized as obsolete, and newer bombers had been limited to just a tail turret, or no gunners at all for several years but the development of several air-to-air missiles, including the Soviet K-5 which began test firings in 1951, eliminated the last justifications for keeping them. In February 1954, the USAF awarded Convair a contract for a new "Featherweight" design program, which significantly reduced weight and crew size. The three configurations were: The six turrets eliminated by Featherweight I reduced the aircraft's crew from 15 to 9. Featherweight III had  a longer range and an operating ceiling of at least , especially valuable for reconnaissance missions. The B-36J-III configuration (the last 14 made) had a single radar-aimed tail turret, extra fuel tanks in the outer wings, and landing gear allowing the maximum gross weight to rise to . Production of the B-36 ceased in 1954. Operating and financial problems. Due to problems that occurred with the B-36 in its early stages of testing, development, and later in service, some critics referred to the aircraft as a "billion-dollar blunder". In particular, the United States Navy saw it as a costly  bungle, diverting congressional funding and interest from naval aviation and aircraft carriers in general, and carrier–based nuclear bombers in particular. In 1947, the Navy attacked congressional funding for the B-36, alleging it failed to meet Pentagon requirements. The Navy held to the pre-eminence of the aircraft carrier in the Pacific during World War II, presuming carrier-based aircraft would be decisive in future wars. To this end, the Navy designed , a "supercarrier" capable of launching huge fleets of tactical aircraft or nuclear bombers. It then pushed to have funding transferred from the B-36 to USS "United States". The  Air Force successfully defended the B-36 project, and "United States" was officially cancelled by Secretary of Defense Louis A. Johnson in a cost-cutting move over the objections of both Secretary of the Navy John L. Sullivan and the Navy's senior uniformed leadership and to which Sullivan resigned in protest. Sullivan was replaced as Secretary of the Navy by Francis P. Matthews, who had limited familiarity with national defense issues, but was a close friend of Johnson. Several high-level Navy officials questioned the government's decision in cancelling the "United States" to fund the B-36, alleging a conflict  of interest because Johnson had once served on Convair's board of directors. The uproar following the cancellation of "United States" in 1949 was nicknamed the "Revolt of the Admirals," during which time Matthews dismissed and forced into retirement the serving Chief of Naval Operations (CNO), Admiral Louis E. Denfeld following the CNO's testimony before the House Armed Services Committee. The congressional and media furor over the firing of ADM Denfeld, as well as the significant use of aircraft carriers in the Korean War, resulted in the Truman administration subsequently ousting both Johnson and Matthews in their respective secretary  roles, and in the design and procurement of the subsequent of supercarriers, which were of comparable size to "United States", but with a design geared towards greater multirole use with composite air wings of fighter, attack, reconnaissance, electronic warfare, early warning and antisubmarine-warfare aircraft. At the same time, heavy manned bombers for the SAC were also deemed crucial to national defense and, as a result, the two systems were never again in competition for the same budgetary resources. Operational history. The B-36, including its GRB-36, RB-36, and XC-99 variants, was in USAF service as part of the SAC from  1948 to 1959. The RB-36 variants of the B-36 were used for reconnaissance during the Cold War with the Soviet Union and the B-36 bomber variants conducted training and test operations and stood ground and airborne alert, but the latter variants were never used offensively as bombers against hostile forces; it never fired a shot in combat. Maintenance. The Wasp Major engines had a prodigious appetite for lubricating oil; each engine required a dedicated 100-gal (380-l) tank. Normal maintenance consisted of tedious measures, such as changing the 56 spark plugs on each of the six engines; the plugs  were often fouled by the lead in the 145 octane antiknock fuel required by the R-4360 engines. Thus, each service required changing 336 spark plugs. Another frequent maintenance job was replacing the dozens of bomb bay light bulbs, which routinely shattered during test firing of the turret guns. The B-36 was too large to fit in most hangars. Since even an aircraft with the range of the B-36 needed to be stationed as close to enemy targets as possible, this meant the plane was largely based in the extreme weather locations of the northern continental United States, Alaska, and the  Arctic. Since the maintenance had to be performed outdoors, the crews were largely exposed to the elements, with temperatures of in winters and in summers, depending on the airbase location. Special shelters were built so the maintenance crews could be given a modicum of protection. Ground crews were at risk of slipping and falling from icy wings, or being blown off the wings by propeller wash running in reverse pitch. The wing roots were thick enough, at , to enable a flight engineer to access the engines and landing gear during flight by crawling through the wings. This was possible only  at altitudes not requiring pressurization. In 1950, Convair (then still Consolidated-Vultee) developed streamlined pods, looking like oversize drop tanks, that were mounted on each side of the B-36's fuselage to carry spare engines between bases. Each pod could airlift two engines. When the pods were empty, they were removed and carried in the bomb bays. No record was made of the special engine pods ever being used. Engine fires. As engine fires occurred with the B-36's radial engines, some crews humorously changed the aircraft's slogan from "six turning, four burning" into "two turning, two burning, two  smoking, two choking and two more unaccounted for." This problem was exacerbated by the propellers' pusher configuration, which increased carburetor icing. The design of the R-4360 engine tacitly assumed that it would be mounted in the conventional tractor configuration—propeller/air intake/28 cylinders/carburetor—with air flowing in that order. In this configuration, the carburetor is bathed in warmed air flowing past the engine, so is unlikely to ice up. However, the R-4360 engines in the B-36 were mounted backwards, in the pusher configuration—air intake/carburetor/28 cylinders/propeller. The carburetor was now in front of the engine, so could  not benefit from engine heat, and also made more traditional short-term carburetor heat systems unsuitable. Hence, when intake air was cold and humid, ice gradually obstructed the carburetor air intake, which in turn gradually increased the richness of the air/fuel mixture until the unburned fuel in the exhaust caught fire. Three engine fires of this nature led to the first loss of an American nuclear weapon when a B-36 crashed in February 1950. Crew experience. Training missions were typically in two parts, a 40-hour flight—followed by time on the ground for refueling and maintenance—and then  a 24-hour second flight. With a sufficiently light load, the B-36 could fly at least 10,000 mi (16,000 km) nonstop, and the highest cruising speed of any version, the B-36J-III, was at 230 mph (380 km/h). Engaging the jet engines could raise the cruising speed to over 400 mph (650 km/h). Hence, a 40-hour mission, with the jets used only for takeoff and climbing, flew about 9,200 mi (15,000 km). Due to its massive size, the B-36 was never considered sprightly or agile; Lieutenant General James Edmundson likened it to "...sitting on your front porch  and flying your house around." Crew compartments were nonetheless cramped, especially when occupied for 24 hours by a crew of 15 in full flight kit. War missions would have been one-way, taking off from forward bases in Alaska or Greenland, overflying the USSR, and landing in Europe, Morocco, or the Middle East. Veteran crews recall feeling confident in their ability to fly the planned missions, but not to survive weapon delivery, as the aircraft may not have been fast enough to escape the blast. These concerns were borne out by the 1954 Operation Castle tests, in which B-36s were  flown at the combat distance from the detonations of bombs in the 15-megaton range. At distances believed typical of wartime delivery, aircraft suffered extensive flash and blast damage. Experiments. The B-36 was employed in a variety of aeronautical experiments throughout its service life. Its immense size, range, and payload capacity lent itself to use in research and development programs. These included nuclear propulsion studies, and "parasite" programs in which the B-36 carried smaller interceptors or reconnaissance aircraft. In May 1946, the Air Force began the Nuclear Energy for the Propulsion of Aircraft project, which was followed in May 1951  by the Aircraft Nuclear Propulsion (ANP) program. The ANP program used modified B-36s to study shielding requirements for an airborne reactor to determine whether a nuclear-powered aircraft was feasible. Convair modified two B-36s under the MX-1589 project. The Nuclear Test Aircraft was a B-36H-20-CF (serial number 51-5712) that had been damaged in a tornado at Carswell AFB on 1 September 1952. This aircraft, designated the XB-36H (and later NB-36H), was modified to carry a , air-cooled nuclear reactor in the aft bomb bay, with a four-ton lead disc shield installed in the middle of the aircraft  between the reactor and the cockpit. A number of large air intake and exhaust holes were installed in the sides and bottom of the aircraft's rear fuselage to cool the reactor in flight. On the ground, a crane would be used to remove the reactor from the aircraft. To protect the crew, the highly modified cockpit was encased in lead and rubber, with a leaded glass windshield. The reactor was operational, but did not power the aircraft; its sole purpose was to investigate the effect of radiation on aircraft systems. Between 1955 and 1957, the NB-36H completed 47 test  flights and 215 hours of flight time, during 89 of which the reactor was critical. Other experiments involved providing the B-36 with its own fighter defense in the form of parasite aircraft carried partially or wholly in a bomb bay. One parasite aircraft was the diminutive McDonnell XF-85 Goblin, which docked using a trapeze system. The concept was tested successfully using a B-29 carrier, but docking proved difficult even for experienced test pilots. Moreover, the XF-85 was seen as no match for contemporary foreign powers' newly developed interceptor aircraft in development and in service; consequently, the project was cancelled. More  successful was the FICON project, involving a modified B-36 (called a GRB-36D "mothership") and the RF-84K, a fighter modified for reconnaissance, in a bomb bay. The GRB-36D would ferry the RF-84K to the vicinity of the objective, whereupon the RF-84K would disconnect and begin its mission. Ten GRB-36Ds and 25 RF-84Ks were built and had limited service in 1955–1956. Projects Tip Tow and Tom-Tom involved docking F-84s to the wingtips of B-29s and B-36s. The hope was that the increased aspect ratio of the combined aircraft would result in a greater range. Project Tip Tow was  cancelled when an EF-84D and a specially modified test EB-29A crashed, killing everyone on both aircraft. This accident was attributed to the EF-84D flipping over onto the wing of the EB-29A. Project Tom-Tom, involving RF-84Fs and a GRB-36D from the FICON project (redesignated JRB-36F), continued for a few months after this crash, but was also cancelled due to the violent turbulence induced by the wingtip vortices of the B-36. Strategic reconnaissance. One of the SAC's initial missions was to plan strategic aerial reconnaissance on a global scale. The first efforts were in photo-reconnaissance and mapping. Along with  the photo-reconnaissance mission, a small electronic intelligence cadre was operating. Weather reconnaissance was part of the effort, as was long-range detection, the search for Soviet atomic explosions. In the late 1940s, strategic intelligence on Soviet capabilities and intentions was scarce. Before the development of the Lockheed U-2 high-altitude spy plane and orbital reconnaissance satellites Corona, technology and politics limited American reconnaissance efforts to the borders, and not the heartland, of the Soviet Union. One of the essential criteria of the early postwar reconnaissance aircraft was the ability to cruise above , a level determined by knowledge of the  capability of Soviet air-defense radar. The main Soviet air-defense radar in the 1950s was the American-supplied SCR-270, or locally made copies, which were only effective up to in theory, an aircraft cruising above this level would remain undetected. The first aircraft to put this theory to the test was the RB-36D specialized photo-reconnaissance version of the B-36D. It was outwardly identical to the standard B-36D, but carried a crew of 22 rather than 15, the additional crew members being needed to operate and maintain the photo-reconnaissance equipment that was carried. The forward bomb bay in  the bomber was replaced by a pressurized, manned compartment that was filled with 14 cameras. This compartment included a small darkroom, where a photo technician could develop the film. The second bomb bay contained up to 80 T-86 photoflash bombs, while the third bay could carry an extra , droppable fuel tank. The fourth bomb bay carried electronic countermeasure equipment. The defensive armament of 16 M-24A-1 20-mm cannons was retained. The extra fuel tanks increased the flight endurance to up to 50 hours. It had an operational ceiling of . Later, a lightweight version of this aircraft, the RB-36-III, could  even reach . RB-36s were distinguished by the bright aluminum finish of the camera compartment (contrasting with the dull magnesium of the rest of the fuselage) and by a series of radar domes under the aft fuselage, varying in number and placement. When developed, it was the only American aircraft having enough range to fly over the Eurasian land mass from bases in the United States, and size enough to carry the bulky, high-resolution cameras of the day. The standard RB-36D carried up to 23 cameras, primarily K-17C, K-22A, K-38, and K-40 cameras. A special 240-inch focal length camera  (known as the Boston Camera after the university where it was designed) was tested on 44-92088, the aircraft being redesignated ERB-36D. The long focal length was achieved by using a two-mirror reflection system. The camera was capable of resolving a golf ball at an altitude and side range of . That is a slant range over . The camera and the contact print of this test can be seen at the National Museum of the United States Air Force at Wright Patterson AFB. The first RB-36D (44-92088) made its initial flight on 18 December 1949, only six months after  the first B-36D had flown. It initially flew without the turbojets. The 28th Strategic Reconnaissance Wing based at Rapid City AFB (later renamed Ellsworth AFB), South Dakota, received its first RB-36D on 3 June 1950. Due to severe material shortages, the new RB-36Ds did not become operationally ready until June 1951. The 24th and last RB-36D was delivered in May 1951. A total of 24 RB-36Ds was built. Some RB-36Ds were later modified to the featherweight configuration, in which all but the tail guns were removed. The crew was reduced from 22 to 19. These aircraft were redesignated as RB-36D -III. Modifications were carried out by Convair from February to November 1954. With a range of , RB-36Ds began probing the boundaries of the Soviet Arctic in 1951. Although on-board equipment indicated detection by Soviet radar, interceptions at the B-36's service ceiling would have remained difficult. RB-36 aircraft operating from RAF Sculthorpe in England made a number of overflights of Soviet Arctic bases, particularly the new nuclear weapons test complex at Novaya Zemlya. RB-36s performed a number of rarely acknowledged reconnaissance missions and are believed to have frequently penetrated Chinese (and Soviet) airspace under the direction of General Curtis  LeMay. In early 1950, Convair began converting B-36As to a reconnaissance configuration; included in the conversions was the sole YB-36 (42-13571). These converted examples were all redesignated RB-36E. The six R-4360-25 engines were replaced by six R-4360-41s. They were also equipped with the four J-47 jet engines that were fitted to the RB-36D. Its normal crew was 22, which included five gunners to man the 16 M-24A-1 20-mm cannon. The last conversion was completed in July 1951. Later, the USAF also bought 73 long-range reconnaissance versions of the B-36H under the designation RB-36H; 23 were  accepted during the first six months of 1952, and the last were delivered by September 1953. More than a third of all B-36s were reconnaissance models. Advances in Soviet air defense systems meant that the RB-36 became limited to flying outside the borders of the Soviet Union, as well as Eastern Europe. By the mid-1950s, the jet-powered Boeing RB-47E was able to pierce Soviet airspace and conduct a variety of spectacular overflights of the Soviet Union. Some of these flights probed deep into the heart of the Soviet Union, taking photographic and radar recordings of the route attacking SAC  bombers would follow to reach their targets. Flights that involved penetrating mainland Russia were termed sensitive intelligence (SENSINT) missions. One RB-47 flew inland and photographed the city of Igarka in Siberia. As with the strategic bombardment versions, the RB-36 was phased out of the SAC inventory beginning in 1956, the last being sent to Davis–Monthan Air Force Base in January 1959. Obsolescence. With the appearance of the Soviet Mikoyan-Gurevich MiG-15 in combat over North Korea in 1950, USAF propeller-driven bombers were rendered obsolete as strategic offensive weapons. Both the B-36 and the B-29/B-50 Superfortresses were designed  during World War II, prior to the jet age. A new generation of swept-wing jet bombers, able to fly higher and faster, was needed to effectively overcome the MiG-15 or subsequent Soviet interceptors if the Cold War escalated into armed conflict. In 1952, while the Korean War was still in full combat, the Convair YB-60, developed from the B-36, entered a design competition with the Boeing YB-52. By early 1953, the Boeing product had emerged as the preferred design. After fighting in Korea had ceased, President Eisenhower called for a "new look" at national defense. His administration chose to  invest in the USAF, especially SAC, retiring nearly all of its B-29/B-50s in favour of the new Boeing B-47 Stratojet, introduced in 1951. By 1955, the B-52 Stratofortress was entering the inventory in substantial numbers, which replaced B-36s. Two major factors contributing to the obsolescence of the B-36 and its phaseout were a lack of aerial refueling capability (instead requiring intermediate refueling bases to reach planned targets deep in the Soviet Union) and its slow speed (making it vulnerable to jet interceptors and thus severely decreasing its likelihood of reaching targets in Soviet territory). The scrapping of B-36s began  in February 1956. Once replaced by B-52s, they were flown directly from operational squadrons to Davis–Monthan AFB, Arizona, where the Mar-Pak Corporation handled their reclamation and destruction. Defense cutbacks in FY 1958 compelled the B-52 procurement process to be stretched out and the B-36 service life to be extended. The B-36s remaining in service were supported with components scavenged from aircraft sent to Davis–Monthan. Further update work was undertaken by Convair at San Diego (Specialized Aircraft Maintenance, SAM-SAC) until 1957 to extend the life and capabilities of the B-36s. By December 1958, only 22 B-36Js were  still operational. On 12 February 1959, the last B-36J built, AF Ser. No. 52-2827, left Biggs AFB, Texas, where it had been on duty with the 95th Heavy Bombardment Wing, and was flown to Amon Carter Field in Fort Worth, where it was put on display. Within two years, all B-36s, except five used for museum display, had been scrapped at Davis–Monthan AFB. Variants. Related models. In 1951, the USAF asked Convair to build a prototype of an all-jet variant of the B-36. Convair complied by replacing the wings on a B-36F with swept wings, from which  were suspended eight Pratt & Whitney XJ57-P-3 jet engines. The result was the B-36G, later renamed the Convair YB-60. The YB-60 was deemed inferior to Boeing's YB-52, and the project was terminated. Just as the C-97 was the transport variant of the B-50, the B-36 was the basis for the Convair XC-99, a double-decked military cargo plane that was the largest piston-engined, land-based aircraft ever built, and the longest practical aircraft of its era. The sole example built was extensively employed for nearly 10 years, especially for cross-country cargo flights during the Korean War . In 2005, this XC-99 was dismantled in anticipation of its being moved from the former Kelly Air Force Base, now the Kelly Field Annex of Lackland AFB in San Antonio, Texas, where it had been retired since 1957. The XC-99 was subsequently relocated to the National Museum of the United States Air Force at Wright-Patterson AFB for restoration, with C-5 Galaxy transports carrying pieces of the XC-99 to Wright-Patterson as space and schedule permitted. A commercial airliner derived from the XC-99, the Convair Model 37, never left the drawing board. It would have been the first "jumbo" airliner . Operators. United States Air Force – Strategic Air Command 2d Air Force 8th Air Force 15th Air Force Note: SAC eliminated tail codes in 1953. Surviving aircraft. only four complete B-36 type aircraft survive from the original 384 produced. Notable incidents and accidents. Though the B-36 had a solid overall safety record, well above average for the class and time, 10 B-36s were involved in accidents between 1949 and 1954 (three B-36Bs, three B-36Ds, and four B-36Hs). A total of 32 B-36s were written off in accidents between 1949 and 1957 of 385 built. When a crash occurred, the magnesium-rich  airframe burned easily. On 14 February 1950 off the northwest coast of British Columbia on Princess Royal Island, 17 crewmen parachuted from their blazing B-36B; 12 crewmen were found with one injured, and five were reported missing. On Labor Day, Monday, 1 September 1952, a tornado hit Carswell Air Force Base, Fort Worth, damaging aircraft of the 7th and 11th Bomber Wings' complement of B-36s. Some two-thirds of the USAF's entire B-36 fleet was affected, as well as six aircraft being built at that point at Convair's Fort Worth plant. The base was shut down and operations  transferred to Meacham Field. Joint repairs by Convair and the USAF got 10 of the 61 B-36s running within two weeks and repaired the other 51 aircraft within five weeks; 18 of 19 heavily damaged aircraft (and the six damaged and unfinished aircraft at Convair) were repaired by May 1953. The 19th (#2051) had to be scrapped, and was used as a nuclear testing site ground target. One heavily damaged aircraft (#5712) was written off and rebuilt as the NB-36H Nuclear Reactor Testbed aircraft. On 18 March 1953, RB-36H-25, 51-13721, flew off course in bad weather and crashed near  Burgoyne's Cove, Newfoundland, Canada (). Brigadier General Richard Ellsworth was among the 23 airmen killed in the crash. B-36s were involved in two "Broken Arrow" incidents. On 13 February 1950, B-36 serial number 44-92075, crashed in an unpopulated region of British Columbia, resulting in the first loss of an American atom bomb. The bomb's plutonium core was dummy lead, but it did have TNT, and it detonated over the ocean before the crew bailed out. Locating the crash site took some effort. On 4 November 2016, however, an object similar to the bomb was reported to have been  located by a diver near the archipelago of Haida Gwaii, off the coast of British Columbia; the Royal Canadian Navy said vessels would be deployed to investigate the object. After investigation, the Royal Canadian Navy determined that it was not the lost bomb. Later in 1954, the airframe, stripped of sensitive material, was substantially destroyed "in situ" by a U.S. military recovery team. On 22 May 1957, a B-36 accidentally dropped a Mark 17 thermonuclear bomb from the control tower while landing at Kirtland Air Force Base in Albuquerque, New Mexico. The weapon had come loose from its mooring and  fell through the bomb bay doors, opening a large hole in the bottom of the aircraft, and sending the aircraft into an uncontrollable climb due to the sudden and unexpected loss of weight. Only the conventional trigger detonated, the bomb being unarmed; the aircraft made a safe landing. These incidents were classified for decades. See list of military nuclear accidents. Notable appearances in media. In 1949, the B-36 was featured in the documentary film, "", about the operations of the 7th Bombardment Wing at Carswell AFB. Other scenes included B-36 production at the Fort Worth plant. "Strategic Air Command" is a  1955 American film starring James Stewart as a Major League Baseball star and World War II veteran who is called back to active duty to become a B-36 pilot and flight commander for SAC. The documentary "Lost Nuke" (2004) chronicles a 2003 Canadian expedition that set out to solve the mystery of the world's first lost nuclear weapon. The team traveled to the remote mountain site of the 1950 British Columbia B-36 crash.