Even before the US entered the war, Germany invaded the Soviet Union and the US Army began to work on the atomic bomb, the US Army Air Force asked Consolidated Aircraft to design a bomber with transcontinental range. This contract was signed on April 11th 1941 and envisioned an airplane that could take off from Gandar Newfoundland and be able to fly to Berlin and back. Consolidated was an airframe builder, in San Diego CA. They built flying boats for the US Navy and designed the B-24 Liberator for the US Air Force. They also built Liberators for the RAF Coastal Command and US Navy and later designed a highly modified naval patrol bomber called the Privater that was based on the B-24. Consolidated also had the B-32 Dominator program, which was a back-up Very Long Range Bomber to the B-29 program.
Design work on the XB-36 was slow, as more pressing needs from World War II was distracting Consolidated's engineers. Yet, on July 23 1943 the US Army Air Force ordered 100 B-36s, before the prototype flew. The XB-36 was rolled out of the San Diego factory on August 20th 1945, but the first flight of this enormous, six motor bomber did not take place until August 20th 1946. If for some reason, the UK or USSR fell to Nazi Germany, the US Air Force planed to bomb Nazi Germany with the B-36. If the situation ever got that dire, the work on the B-36 program would have been sped up. As it was, it was a low priority project during World War II and the B-36 did not enter squadron service until the summer of 1949. It was the backbone of the Strategic Air Command of the US Air Force, during the early Cold War. The last B-36s were taken out of service by the US Air Force in 1959, when the jet powered B-52 replaced them as SAC's main bomber.
Source: "Convair B-36: A Comprehensive History of America's "Big Stick" by K Jacobsen Meyers. Note: Consolidated merged with the Vultee aircraft company in 1943 and changed its name to Convair.