The initial contract (W535-ac-22352) of 15 November 1941 met Consolidated's terms. On 22 November, 7 days after the contract's approval, Wright Field Engineering Division concluded that the 6 engine rather than the 4 engine design should be adopted. This posed no problem, since it had been one of the options offered by Consolidated. On 10 December, 10 Model 35 was redesignated Model 36 to avoid confusion with the Northrop "flying wing;" by then known as the B-35. There was yet no sign of the difficulties soon to come.
After more than 6 months had been spent in refining the chosen design, exerting every effort to control weight, reduce drag, and eliminate the various developmental kinks of a new airplane, the B-36 mockup was inspected on 20 July 1942. Controversy generated by the inspection nearly caused cancellation of the experimental program. The Mockup Committee wanted to reduce firepower and crew to make the B-36 meet its 10,000 mile range requirement. But some members argued that such changes would render the airplane tactically useless and in fact superfluous, since the Experimental Engineering Division already had a "flying laboratory" (XB-19). If these reductions were necessary, the AAF should stop the project and channel the manpower into more productive bomber programs. The Mockup Committee eventually agreed to delete "less necessary" items of equipment from the aircraft. This reduced weight and saved the future B-36 at least temporarily.
A month after inspection of the B-36 mockup, Consolidated suggested shifting the XB-36 project from San Diego, California, to its new government leased plant in Fort Worth, Texas. Even though the move was completed in September 1942, less than 30 days after being approved by the AAF, development was set back several months. Innumerable problems remained to be solved, but Consolidated asked the AAF to place a contract for a production quantity of the new aircraft. The contractor claimed that 2 years could be pared from the development cycle if preliminary work on production B-36s started without waiting for completion of the experimental planes. Consolidated's request was ill timed. Military setbacks during 1942, especially in the Pacific, plus the fact that even under the best circumstances the B-36 could not soon become operational, prevented the AAF from diverting scarce resources for its production.
Another Consolidated request in the summer of 1942 fared somewhat better. The AAF agreed to development of a cargo configuration of the XB-36, provided that 1 of the 2 experimental bombers was produced at least 3 months ahead of the cargo plane (referred to as the XC-99). Consolidated actually wanted the XC-99 to test the engines, landing gear, and flight characteristics of the forthcoming XB-36s. The contractor also believed the XC-99 could be ready to fly much sooner than either of the 2 XB-36s because armament and other military gear would be left out. The AAF conditions were accepted, however, and a $4.6 million contract was approved by year's end." The proposed C-99 could have carried 400 fully equipped troops or more than 100,000 pounds of cargo, but only a single XC-99 was built. It was delivered in 1949 and remained in the inventory until 1957.
Engineers continued to wrestle with weight increases and various developmental troubles. The B-36's twin tail was to be deleted in favor of a single vertical one. This would decrease weight by 3,850 pounds, stabilize direction, and lower drag. The modification was approved on 10 October 1943, when the initial development contract (W535 ac 22352) was amended by Change Order No. 7. This change order (previous ones were insignificant) also allowed the contractor a 120 day delay in delivery. So at best the AAF would not get its first XB-36 until September 1944. War problems suddenly boosted the importance of the B-36 however. Military setbacks that had hampered the program in 1942 assumed a new dimension in the spring of 1943 as China appeared near collapse. The B-17 and the B-24 had insufficient range to operate over the vast distances of the Pacific. The Boeing B-29 was in the early stage of production, but was experiencing more problems than usual. The parallel development of the Convair B-32 (Consolidated until mid March), generally considered by AAF as an "insurance plane;' in case the B-29 failed, did not progress as well as hoped for. The B-32 seemed much less promising than the B-29, on which higher priorities had been concentrated. Moreover, even if production delays could be overcome, neither of these planes could reach Japan, for battles had to be won before the Mariana Islands could become a base for B-29 or B-32 operations. Speeding up B-36 development might provide a way, possibly the only one, for attacking the Japanese homeland and at least would immediately bolster Chinese morale. The war in the Pacific dominated the discussion at the "Trident" conference of President Roosevelt and Prime Minister Churchill in May 1943 Lt. Gen. Joseph W. Stilwell and Maj. Gen. Claire L. Chennault both confirming that the situation in China was desperate. Ensuing talks between Secretary of War Henry L. Stimson, Assistant Secretary of War Robert P. Patterson, and high ranking officers of the AAF, led Secretary Stimson to waive customary procurement procedures and to authorize the AAF to order B-36 production without awaiting completion and testing of the 2 experimental planes then under contract. Therefore, on 19 June General Arnold directed procurement of 100 B-36s. General Arnold became Commanding General of the AAF in March 1942 and was promoted to 4 star general 1 year later. His order, however, would be cut back or canceled in the event of excessive production difficulties. The AAF letter of intent for 100 B-36s was signed by Convair on 23 July.
In spite of its elevated status, the B-36 program made scant progress. Essential wind tunnel tests of the new design were postponed until the spring of 1944, because other projects had retained higher priorities and no alternate testing facilities were available. Meanwhile, besides usual engineering difficulties, Convair was greatly concerned over the growing weight of the Pratt & Whitney X Wasp engine selected for the experimental B-36. In Convair's opinion, tying the XB-36 to a single engine design was a mistake. Yet, further study of the Lycoming BX liquid cooled engine (noted for lower fuel consumption) had been discontinued on the belief that development of the BX engine would demand manpower, materiel, and facilities that could not be spared. The AAF also insisted that development of a new engine would only delay "expeditious prosecution"of the B-36 design. In any case, before much of anything could be done, the B-36 was relegated to a secondary position. This time, the Convair B-32 had to come first. The military situation in the Pacific improved materially by mid 1944. The Marianas campaign neared its successful conclusion, and the forthcoming use of bases on Saipan, Tinian, and Guam urgently called for medium range bombers. Production troubles with the B-29 were almost solved, and it was now left to Convair to accelerate the B-32 program. B-36 work would continue, but only as a safety measure.
The letter of intent of 23 July 1943,supplemented by Letter Contract W33-038 ac-7 on 23 August 1943, gave way 1 year later to a definitive contract. Interestingly, the US. Government was not liable should a letter of intent be canceled. This was not so for the more often used letter contract which obligated funds. The final $160 million contract (including a $6 million fixed fee and the cost of all spare parts and engineering data) continued to cover the production of 100 B 36s, but no longer carried any priority rating. Delivery schedules, however, were unchanged. The first B-36 was due in August 1945; the last, in October 1946. Not surprisingly, these delivery dates were subsequently changed, as was the $160 million contract-increased by $61 million on 26 August 1946, when Change Order No. 10 was approved.
With victory in sight (The German surrender was officially ratified in Berlin on 8 May 1945; Japan surrendered unconditionally on 14 August, but the Japanese Emperor did not sign the Potsdam requirements for surrender until 2 September.), war contracts were scrutinized for cancellation or drastic cutback. Aircraft production was actually cut by 30 percent on 25 May, a reduction of 17,000 planes over an 18 month period. The review left the B-36 contract untouched. There was no question that a long range bomber was needed. The proof was in the terrible price paid in lives and materiel to win advanced bases in the Pacific. The atomic bomb, unlikely to remain an American monopoly, was another strategic justification. Inasmuch as U.S. retaliation would have to be quick, there would be no time for conquering faraway bases. And, realistically, a long range bomber could be the best war deterrent for the immediate future. From the economic standpoint, the B-36 also looked good. It out performed the B-29 and the B-35 "flying wing" for long range missions and was cheaper by half to operate than the B-29 in terms of cost per ton per mile. On 6 August 1945, General Arnold approved the Air Staff recommendation to keep the B-36 production contract intact. Lt. Gen. Hoyt S. Vandenberg, then Assistant Chief of Air Staff for Operations, Commitments, and Requirements, advocated formation of 4 "Very Heavy" groups equipped with B-36s to constitute an "effective, mobile task force for our postwar air force." General Vandenberg's recommendation was embodied in the AAF's postwar 70 group program. This program remained a constant, though unreachable goal until the start of the Korean War.
While the fate of the B-36 program vacillated with changing wartime priorities, the aircraft's development remained painfully slow. By 1945 Convair still worried over the weight of the R 4360 25 engine Pratt & Whitney's third version of the original X Wasp. Adding nose guns required extensive rearrangement of the forward crew compartment. A mockup of the new nose section had been approved in late 1944 and would become a prototype nose for the second XB-36. Yet, the radio and radar equipment in the new nose would augment gross weight by at least 3,500 pounds more, if the antenna. of the AN/APQ 7 radar could not be installed in the leading edge of the wing. This and the 2,304 pound increase for the 6 new engines could present a serious problem. Nor was it easy to select wheels for the aircraft's landing gear. The rationale for dual main wheels was simplified maintenance without a need for special tools. The single wheel type had other merits. These arguments ended in mid 1945 when Maj. Gen. Edward M. Powers, Assistant Chief of Air Staff for Materiel, Maintenance, and Distribution, recommended that a new landing gear be devised to distribute the aircraft weight more evenly, thus reducing the need for specially built runways. The four wheel truck type gear eventually adopted was 1,500 pounds lighter than the one previously considered. It also enabled the B-36 to use any airfield suitable for the B-29.
Meanwhile, faulty workmanship and use of substandard materials were discovered in the experimental B-36. AAF inspectors also noted the dearth of qualified workers at the beginning of the project and the failure of the airfoil contour of the aircraft wing to conform to specifications. In fairness to Convair, substituting materials was a generally accepted practice in urgently awaited experimental planes. As for other discrepancies, the contractor was not altogether to blame but promised to correct them promptly. Progress was made, but labor strikes at the Fort Worth plant in October 1945 and in February 1946, a normal part of postwar adjustment, delayed the program for several months. On 25 March General Powers indicated that the structural limitations of the forthcoming XB-36 might make it useless, other than as a test vehicle for the initial flight.
In spite of every effort, the all metal, semimonocoque XB-36 did not fly until almost 6 years after signature of the development contract. The initial 37 minute flight of 8 August was deemed successful, but the wing flap actuating system and the aircraft's overall performance fell below the original expectations. Besides its known structural limitations, the XB-36 had an already obsolete single wheel landing gear, carried only a minimum of components, and lacked the nose armament designed for the second XB-36. Still, a beginning had been made. After being grounded in late 1946 for modification, the XB-36 was test flown for 160 hours by pilots of the Air Materiel Command (AMC). The lineage of AMC reflected the many reorganizations following the establishment on 17 July 1944 as the AAF Materiel and Services Command (Temporary), the parent organization. On 31 August 1944, the Materiel and Services Command (Temporary) became the AAF Air Technical Service Command, which became the Air Technical Service Command on 1 July 1945. AMC was created on 9 March 1946, and on 1 April 1961, it became Air Force Logistics Command. The plane was then sent to the contractor for further testing (Convair pilots made 53 test flights with the XB-36 (Serial Number 42-13570), logging a total of 117 flying hours), and the United States Air Force (USAF) retrieved it in mid 1948. (The United States Air Force was established on 26 July 1947, when the National Security Act of 1947 became law. It began functioning as a separate service, coequal with Army and Navy, on 18 September 1947.) As predicted by General Powers, the experimental B-36 had limited operational value and was used by the Strategic Air Command (SAC) for training. The Strategic Air Command was established by the Army Air Forces on 21 March 1946.