The U.S. military was convinced in 1941 that an intercontinental bomber was desperately needed.
In mid-941, it looked as if the Axis powers might sweep over the entire Eurasian landmass. The Germans had been stopped at the English Channel the previous summer, but they and their Italian allies had nearly pushed the British out of the eastern Mediterranean and North Africa, the gateway to the Middle East and India. On the other side of the world, Japan had already conquered one-third of China and clearly had designs on French Indochina and the rest of the Pacific Rim. It was entirely possible, therefore, that the United States would soon find itself completely hemmed in by hostile nations, with no access to operating bases outside the Western Hemisphere.
These international conditions imposed upon the American military planning establishment a serious dilemma. The Boeing XB-29, even if it achieved its projected performance, would be of little value without overseas bases. What was needed was a bomber of truly intercontinental range, one capable of reaching targets in Europe or Asia from bases within the North American continent.
In early 1941, U.S. Army Air Corps officials met in secret with the Boeing Airplane Company, Consolidated Aircraft Corporation, Douglas Aircraft Company and Northrop Aircraft Inc. to solicit proposals for an all-new bomber design. The competition called for an aircraft with a maximum speed of 450 mph, an operational ceiling of 45,000 feet and a combat radius, with 10,000-pound bombload, in excess of 5,000 miles. It would be expected to perform this mission while cruising 275 mph at 25,000 feet, and be able, over shorter distances, to carry an additional bombload of up to 72,000 pounds. Needless to say, the technology for such an aircraft did not exist at the time.
The Army Air Corps (soon to become the virtually autonomous U.S. Army Air Forces), led by Maj. Gen. Henry H. “Hap” Arnold and his band of idea men, felt that if anybody was able to close this technology gap, the four companies selected to participate in this project could do it. For Boeing, the situation was toughest: In addition to the urgent priority assigned to the XB-29 program, it was tooling up to build B-17s by the thousands. Consolidated had its plate full, too, with PBYs and B-24s in production and the XB-32—a backup design to the B-29—under development. From the outset, Douglas’ participation was limited to development and testing of the experimental Allison V3420 V24 engine for use as a bomber power plant. Northrop had specifically been told to approach the project from a different angle—to develop a proposal based on its flying wing concepts. John K. “Jack” Northrop, the founder of the company, had been experimenting with flying wing designs since 1923 and had flown the N-1M flying wing demonstrator in 1940.
Given the unheard-of performance that was expected from this airplane, the companies involved weren’t exactly falling all over each other to present their ideas. In May 1941, Consolidated had submitted some preliminary thoughts on a very large airplane—even larger than the Douglas XB-19—but that’s as far as it went. Then in August 1941, to get the project moving, the USAAF reduced the performance requirements to a 4,000- mile combat radius, a service ceiling of 40,000 feet, and a cruising speed in the vicinity of 250 mph. That same month, General Arnold traveled to the Northrop plant in California to see how progress was coming on the flying wing. After a follow-up meeting with the companies, the USAAF brass concluded that Consolidated’s design concept showed the most potential. In November 1941, the company was given a contract to proceed with further design development and mockup construction and to build two prototypes under the designation XB-36. Delivery of the first prototype was slated for May 1944. A week later Northrop was awarded a similar contract to build a prototype for the XB-35 flying wing that would be preceded by a one-third scale proof of concept aircraft known as the N-9M. The time set for delivery of the XB-35 was two years, in November 1943. Now the hard part would begin.
Consolidated’s XB-36 design team, led by Harry A. Sutton as chief engineer, settled on a six-engine pusher layout as the plane’s form and dimensions began to take shape. The size would be unprecedented: a wingspan of 230 feet incorporating a total area of 4,772 square feet (greater than the B-29 by a factor of 2.7) and a fuselage length of 163 feet; loaded weight, however, was still a matter of conjecture. The wings would be moderately swept back and shoulder mounted to a circular-section fuselage. Power would come from six Pratt & Whitney R4360s, 28-cylinder, four-row air-cooled radial engines driving 19-foot-diameter, three-bladed Curtiss electric propellers. The engines, which at the time existed only in concept, were each expected to deliver 3,000 hp. A twin fin and rudder layout similar to that of the B-24 and XB-32 was initially adopted as the empennage configuration. To withstand the extremes of temperature and pressure at higher altitudes, the crew would be housed in two pressurized compartments, one in the nose and one in the tail of the long fuselage, connected by an 80-foot-long, 25-inch-wide pressurized tunnel that would utilize a wheeled trolley to facilitate crew movement between compartments.
At Northrop’s plant detailed design work was proceeding on the XB-35 flying wing, and a full-scale mockup was completed by July 2, 1942. The USAAF was sufficiently impressed to order an additional 13 YB-35 service test examples in December. The airplane was radical—emerging as an “all wing” design (i.e., no vertical flying surfaces of any kind) spanning 172 feet from tip to tip, swept back 27 degrees from the leading edge, with a chord width of 37 feet at the center. The only protuberances marring the wing’s surface were the four gun barbettes containing defensive armament, a bubble canopy for the pilot, navigator and flight engineer, a tail cone extending aft of the trailing edge centerline to house a portion of the nine-man crew, and the fairings over shafts leading to the propellers. Power would be supplied by four “buried” pusher-mounted Pratt & Whitney R4360 engines, coupled to long drive shafts driving contrarotating propellers. Yaw control would be achieved through split flaps on the wing’s trailing edges near the tips, and pitch and roll would be controlled by elevons— interlinked to function as both elevators and ailerons.
When USAAF officials met with Consolidated in July 1942 to inspect the completed XB-36 mockup, the whole project came within a hairsbreadth of being canceled. The USAAF people felt that projected weight, stemming mainly from the defensive armament and equipment planned, was leading the XB-36 down the same path as the Douglas XB-19—too heavy and too slow to perform the intended mission. After a hard round of arguments and threats, Consolidated agreed to make a number of weight-saving changes, and the project was saved—for the time being anyway.
In the spring of 1943, with China appearing on the verge of collapse, the USAAF feared that Operation Matterhorn—the plan to use B-29s to bomb Japan from bases in central China—might be abandoned, leaving the longer-range B-36 as the only viable means of striking the Japanese Home Islands. Work on the XB-36 was continuing slowly because Consolidated, with heavy commitments on other wartime contracts, had little space or time to devote to what was essentially a research and development program. When urged to speed up development, Consolidated suggested that a production contract would be necessary in order to dedicate the essential space, staff and subcontractor support. On June 19, 1943, at General Arnold’s express direction, the USAAF awarded a contract for 100 B-36 production models. Under the new schedule, the XB-36 was supposed to fly by September 1944, with delivery of production models to begin by August 1945.
Northrop had begun flight-testing with its first one-third scale prototype (N-9M-1) in late December 1942, and three more were ordered while testing was underway. The test program, while demonstrating the validity of Northrop’s aerodynamic concept, was marred by problems related to the engines and drive shafts, resulting in a fatal crash of the first prototype in May 1943. Northrop had internal problems too—although Jack Northrop had been designing aircraft since 1916, his company was relatively new and lacked the facilities to engage in large-scale bomber production. When the contract for 200 B-35s was formally issued on June 30, 1943, Northrop agreed to build the two XB-35 prototypes and 13 YB-35s at its own plant, but actual B-35 production was farmed out to the Glenn L. Martin Company, with deliveries scheduled to start in June 1945.
By mid-1944, however, the inter- continental bomber project was seriously behind schedule. Delays in the delivery and testing of the R4360 engines had been partially responsible and, in the case of the XB-36, wind tunnel testing had been postponed until the spring of 1944 because there were programs ahead of it. And the project’s sense of urgency had dramatically changed— the B-29s had arrived in the CBI (China-Burma-India) Theater, and new bases were planned in the Marianas Islands. Meanwhile, Martin informed the USAAF and Northrop that due to severe shortages of experienced manpower, it would be unable to deliver any production B-35s until sometime in 1947. The production order for 100 B-36s was retained at a lower priority, but except for two XB-35 prototypes and the 13 YB-35s, the flying wing contract was canceled.
World War II ended before either one of the prototypes flew. In August 1945, while wartime aircraft production contracts were experiencing wholesale cancellations, the Air Staff (the USAAF’s chief planning body) recommended that the B-36 contract be kept intact. Many on the staff believed the new atomic bomb would call for a very long-range delivery system that was not dependent on overseas bases. As to the flying wings, the project was considered sufficiently worthwhile to pursue for research and development reasons, even if the aircraft were never used operationally.
The Northrop and Convair (Consolidated’s name following a merger with Vultee) prototypes made their maiden flights within six weeks of each other. The XB-35 flew first, taking off on June 25, 1946, in a 45-minute flight from the Hawthorne plant near Los Angeles to Muroc Dry Lake. The enormous XB-36 prototype had been completed with a single vertical fin assembly that towered nearly 47 feet above the ground, and sat on single 110- inch-diameter tires. Only three runways in the entire United States were thick enough to withstand its weight. On August 8, the XB-36 lifted off the runway at Fort Worth, Texas, for a 37- minute flight. Texans must have been proud—the biggest and heaviest landplane in the world taking off in the biggest state.
The XB-35 test program ran into immediate difficulties. Serious malfunctions in the engine gearboxes and in the control mechanisms for the huge contrarotating propellers grounded the prototype in September 1946 after only 19 flights had been made. The same problems were encountered with the second XB-35 prototype, which was grounded after only eight flights. The problems with the contraprops and their gearboxes were never solved, so that by late 1947, a decision was made to switch them and the preproduction YBs to single-rotation propellers. By the time the first YB-35 with new single-rotation propellers flew in May 1948, the piston-engine flying wing program was doomed. But the flying wing itself was not dead—it had been given a new lease on life in June 1945 when the USAAF ordered two of the YB-35s to be modified for the installation of the new Allison J35 turbojet engines.
In early testing of the XB-36 prototype, overall performance fell below design expectations. Most significantly, altitudes over 30,000 feet could not be maintained for any length of time because of engine overheating, reducing both range and airspeed. There was an assortment of other problems (not surprising in a plane this complex) related to operation of the wing-flap mechanisms, electrical wiring and vibration in the shaft-driven propellers. The prototype was almost lost in March 1947 because of an engine fire right after takeoff, but the pilots managed to bring it in for a safe landing after spending three hours in the air to burn off excess fuel.
There were sharp differences within the USAAF hierarchy as to the B-36’s suitability for production. In late 1946, General George Kenney, head of the newly formed Strategic Air Command (SAC), suggested that the B-36 contract be reduced to only a few service test aircraft, arguing instead for a step-up in the Boeing B-50 program (a development based upon the well-proven B-29 airframe). But the Air Staff, supported by General Nathan F. Twining, contended that such a move would be premature in light of the limited test period with only one prototype, and General Carl Spaatz, the new chief of the USAAF (soon to become the wholly separate U.S. Air Force), finally ended the argument in favor of B-36 production.
The YB-36, the second prototype, featured a completely redesigned nose section with a high-visibility canopy and incorporated many other refinements learned from experience with the XB-36. When it flew on December 4, 1947, it outperformed the XB-36 in virtually every category and would become the template for future production models. Production versions would also be equipped with a double-bogie, four-wheel main landing gear that would replace the one-tire units that restricted operations from most runways. The B-36B would become the first full-scale production version (the B-36As were used for operational testing and training) and differed from previous models in having 3,500-hp R4360-41 engines with water injection and better electronic components, including the new AN/APQ-24 radar bombing/navigation system. Maximum loaded weight had risen to an incredible 328,000 pounds. It possessed the most formidable armament ever fitted to any warplane: six retractable turrets, each equipped with a pair of remotely fired 20mm cannons, plus two more 20mm cannons apiece in the nose and tail positions (approximately 2.2 times the firepower of a standard B-29). Performance of B-36B production models was even better than expected—a top speed of 381 mph, a service ceiling of 42,500 feet and a 3,740-mile combat radius at a combat weight of 227,700 pounds. It had been a long time coming, but the intercontinental bomber had arrived.
Delivery of the B-36B to operational SAC units began in November 1948, with the last one delivered in September 1950. To say that the B-36s were fully operational at this point, however, would be an exaggeration. For the next three years or more, the planes were still essentially under development, undergoing continuous upgrades and modifications.
Meanwhile, the airframes of the second and third YB-35s had been modified for installation of eight Allison J35-A-5 turbojet engines, each delivering a maximum thrust of 4,000 pounds. To compensate for the loss of vertical stability caused by removal of the engine drive shaft fairings, four pairs of small vertical fins were added to the wing’s trailing edge. All armament except the tail cone guns was eliminated. Completion of the YB-49 prototype was originally scheduled for June 1946, but unforeseen problems in making the many aerodynamic and structural changes needed delayed the program another year. The flight of the first YB-49 was made on October 21, 1947, when it was flown out to Muroc Dry Lake to continue the test program; the second prototype flew three months later.
In its initial trials, the YB-49 attained a maximum speed of 520 mph and a service ceiling of 42,500 feet. Combat radius with a 10,000-pound bombload was 2,000 miles, about one-half the range of the piston-engine XB-35. During operational evaluations, USAAF test pilots considered the YB-49 difficult to fly and rated it as an unstable bombing platform. The program was further set back in May 1948 when the second YB-49 crashed, killing Air Force test pilot Captain Glenn Edwards and his crew. The actual cause of the crash was never determined. In April 1949, with a total of 44 flights and approximately 120 hours of flight-testing completed, the YB-49 program was abruptly terminated. Before that happened, a parallel program had been created in mid-1948 for development of a photoreconnaissance version of the jet flying wing, designated the YRB-49A, which featured a six-engine layout with two of the J35s pylon-mounted in nacelles beneath the wings. That aircraft flew on May 4, 1950, but by then the entire flying wing program was as dead as a dodo.
After General Curtis LeMay assumed command of SAC in October 1948, he became convinced that a much larger fleet of B-36s would be needed to provide the United States with a nuclear deterrent well into the 1950s. Convair had in fact proposed a new version, the B-36D, in which two pairs of General Electric J47 turbojet engines would be pod-mounted below the outer wing. This upgrade was expected to increase top speed by 100 mph and reduce takeoff roll by 2,000 feet (allowing operations from more bases). The Air Force wanted to improve its existing fleet of B-36Bs to this standard and add more new B-36Ds to the SAC inventory. At the same time, the Navy had plans to build a new supercarrier (CVA-58), which it viewed as a launching platform for a mobile nuclear strike force. President Harry Truman’s 1949 defense budget plans, however, didn’t include money for both.
In April 1949, Secretary of Defense Louis Johnson abruptly terminated the super carrier program and approved the Air Force plan to develop a fleet of B-36Ds. The Joint Chiefs of Staff had previously decided that the Air Force was to have primary responsibility for the nuclear mission, but the hue and cry raised over the cancellation of the carrier led to hearings before the Senate Armed Services Committee in the summer of 1949. At issue were charges of misdeeds between the Air Force and Convair and the propriety of the B-36 as the nation’s chief nuclear weapons delivery system. As a side matter, there was some debate over whether the YB-49 flying wing had been given a fair evaluation. Jack Northrop testified at the time that he believed the Air Force’s decision to cancel his project had been made in good faith. In any case, the investigation subsequently cleared the Air Force and Convair of the charges and confirmed the Department of Defense’s decision to proceed with the B-36.
Starting in 1952, the B-36D and succeeding versions (383 total production) formed the mainstay of SAC’s long-range bomber force until replaced by the Boeing B-52. The last operational B-36 was retired in 1959.
In 1970 Jack Northrop told an interviewer that he had deliberately lied in the Senate hearings to avoid repercussions from the Air Force—that the real reason for cancellation of the YB-49 program had been his earlier refusal to merge his company with Convair. Truth? Sour grapes? And the government’s decision to put all its eggs in one basket—to rely solely on the B-36 as America’s long-range nuclear deterrent? Fortunately for us—and the rest the world—the decision was never put to the test.
E.R. Johnson, who writes from Mountain Home, Ark., is a frequent contributor to Aviation History. For additional reading, try: American Warplanes, by Bill Gunston; U.S. Bombers, B-1 to B-70, by Lloyd S. Jones; or Post World War II Bombers, published by the Office of Air Force History.
Originally published in the May 2006 issue of Aviation History. To subscribe, click here.