B-36 bomber was one of the largest propeller-driven aircraft ever built. Designed during WW2 it was intended to bomb Germany from the US, but was not finished in time, and ended up as a nuclear bomber in the Cold War.
In the first months of 1941, things were looking bleak for the United States. Although not officially involved in the Second World War that was already raging in Europe, President Franklin Roosevelt knew that eventually he would have to fight Hitler. And, in 1941, it seemed likely that he would have to do it alone. France had already fallen the year before. England had barely survived the Battle of Britain and was being pounded by the Blitz, and in June 1941 Hitler’s troops drove deep into Russia.
It looked increasingly likely that the United States might be the only remaining democracy, and with the loss of France, Britain and Russia, the US may have been forced to wage a long-distance war from North America. The Army Air Force had just deployed the new B-17 Flying Fortress and B-24 Liberator heavy bombers, and work was already being begun on the prototypes for the planned B-29 Superfortress, but none of these had anything near the capability to strike across the Atlantic.
So in the spring of 1941 the Pentagon issued a “Request for Proposals” for a new and gigantic bomber: one capable of cruising at 275mph (with top speed of 450mph—fast enough to outrun any German fighter), a maximum altitude of 45,000 feet (higher than any fighter plane or anti-aircraft fire could reach), a range of 12,000 miles (enough to reach Germany from bases in the US), and a payload of 10,000 pounds of bombs. This was, quite simply, impossible with the technology of the day, and in August the requirements were dropped to a range of 8,000 miles and an altitude of 40,000 feet.
In response, the Consolidated Aircraft Company submitted a design for a truly immense airplane, dubbed the XB-36—230 feet in wingspan and with six engines. In November 1941, the Army asked Consolidated to produce two prototypes.
On December 7, however, Japan attacked Pearl Harbor, and the United States found itself in a war for which it was unprepared. The B-24 was desperately needed in the Pacific, and Consolidated was ordered to give its priority to turning out Liberators as fast as it could. The XB-36 project was put on hold.
By 1943, the war in the Pacific had been turned around, and the Pentagon made plans to begin bombing the cities of Japan with B-29 bombers based in China. But the Chinese forces under Chiang Kai-shek proved unable to deal with the Japanese, and when the planned locations for the bomber bases were overrun by a Japanese offensive, it appeared that, with China unavailable, the US might now need to bomb Japanese cities from bases in Hawaii. The only plane with any such capability was the XB-36. So in July 1943, even though a prototype had not even been tested yet, the Pentagon placed an immediate order with the Convair Company (formed when Consolidated merged with Vultee) for 100 combat-ready B-36s (dubbed “Peacemakers”) for delivery by the summer of 1945, in time for the planned invasion of Japan in November.
It was a tall order. Nearly everything about the plane was new, and it had numerous kinks to work out. Delays resulted when the original twin-rudder tail was changed to a single fin, then again when the landing gear had to be re-worked. The swept-wings had trouble dealing with the aerodynamic forces they encountered, and the capacious fuel tanks inside often leaked when the seals popped under the constant flexing of the wings. There were problems with the remotely-operated electric gun turrets, and eventually they were dropped, leaving just a tail gunner.
The biggest difficulties were with the engines. Unlike other bombers, the B-36’s six 28-cylinder Pratt & Whitney R-4360 Wasp Major engines were configured as “pushers”—they were built into the rear edge of the wing and faced backwards. They were supposed to be cooled by air directed from inlets in the leading edge of the wing, but this system never worked well and the engines constantly overheated. Fires were common and, since much of the engine was made of magnesium, produced spectacular and destructive flames that burned white hot.
In the end, the delays did no harm. When US troops captured Saipan, it put Japan within range of the B-29 Superfortresses, and atomic bombs carried from Tinian forced a surrender. The B-36 Peacemaker missed the war, and was not ready for flight (with smaller engines because the Wasp Majors were still not ready) for another year. Only 22 of the initial B-36A models were delivered. The B-36B, with improved Wasp Major engines, followed, and the first combat-ready bombers were deployed in 1948.
Meanwhile, the end of the Second World War graded almost immediately into the beginning of the Cold War. The US Air Force came into being, and the Strategic Air Command was organized as the tip of the American military spear, capable of delivering atomic bombs in response to any Soviet attack. But it was soon apparent that piston-engine technology was now obsolete, and plans were already being made to replace the B-36 with an all-jet nuclear bomber, the B-47. As it turned out, the B-47 was itself delayed by technical difficulties and was not ready until 1953. An even larger jet bomber, the B-52, existed only on paper. And when the hydrogen bomb was developed in 1951, only the B-36 was big enough to carry it. And so, despite its obsolete design, the Peacemaker was forced into the role of SAC’s primary intercontinental nuclear bomber.
A new B-36D model was hastily rolled out, fitted with a pod at the tip of each wing that contained two General Electric J47-19 jet engines (the pods were also retrofitted to the existing B models). With “six turning and four burning”, the B-36 now produced 40,000 horsepower, although the jets were used only for takeoffs and for rapid dashes over the target. With bomb bays capable of holding over 85,000 pounds, the B-36D could deliver any nuclear bomb in the US arsenal.
By the time of the Korean War, a reconnaissance version of the B-36 had appeared, many of which were old A models which replaced the nuclear weapon in the forward bomb bay with a large camera with 18-inch film. There were a whole series of secret photographic flights over the Soviet Union. A new J model bomber appeared, and one B-36 was specially modified for use in a secret program to produce a nuclear-propelled airplane. In 1955, the airplane was featured in a USAF-approved Hollywood film, “Strategic Air Command”, starring Jimmy Stewart.
But by 1956 the Peacemaker had outlived its usefulness, and was being replaced by the new B-52. By 1959 there were no longer any B-36s in service.
Today there are only a handful of B-36’s on display. The US Air Force Museum in Dayton has a J model on display, as does the Castle Air Museum in California. The Pima Air and Space Museum in Arizona has the last B-36 to roll off the production line, a J model belonging to the USAF Museum named the “City of Ft Worth”. It was on display in Texas for a time before being sent on loan to Pima.
Hidden History 
It is one seriously big-ass bird.
There’s a video or two on youtube chronicling the restoration of the Fort Worth aircraft. That was some project.