Boeing B-29 Superfortress in the context of "509th Composite Group"

Air warfare was a major component in all theaters of World War II and, together with anti-aircraft warfare, consumed a large fraction of the industrial output of the major powers. Germany and Japan depended on air forces that were closely integrated with land and naval forces; the Axis powers downplayed the advantage of fleets of strategic bombers and were late in appreciating the need to defend against Allied strategic bombing. By contrast, Britain and the United States took an approach that greatly emphasized strategic bombing and (to a lesser degree) tactical control of the battlefield by air as well as adequate air defenses. Both Britain and the U.S. built substantially larger strategic forces of large, long-range bombers. Simultaneously, they built tactical air forces that could win air superiority over the battlefields, thereby giving vital assistance to ground troops. The U.S. Navy and Royal Navy also built a powerful naval-air component based on aircraft carriers, as did the Imperial Japanese Navy; these played the central role in the war at sea.

On 6 and 9 August 1945, the United States detonated two atomic bombs over the Japanese cities of Hiroshima and Nagasaki, respectively, during World War II. The aerial bombings killed 150,000 to 246,000 people, most of whom were civilians, and remain the only uses of nuclear weapons in an armed conflict. Japan announced its surrender to the Allies on 15 August, six days after the bombing of Nagasaki and the Soviet Union's declaration of war against Japan and invasion of Manchuria. The Japanese government signed an instrument of surrender on 2 September, ending the war.

In the final year of World War II, the Allies prepared for a costly invasion of the Japanese mainland. This undertaking was preceded by a conventional bombing and firebombing campaign that devastated 64 Japanese cities, including an operation on Tokyo. The war in Europe concluded when Germany surrendered on 8 May 1945, and the Allies turned their full attention to the Pacific War. By July 1945, the Allies' Manhattan Project had produced two types of atomic bombs: "Little Boy", an enriched uranium gun-type fission weapon, and "Fat Man", a plutonium implosion-type nuclear weapon. The 509th Composite Group of the U.S. Army Air Forces was trained and equipped with the specialized Silverplate version of the Boeing B-29 Superfortress, and deployed to Tinian in the Mariana Islands. The Allies called for the unconditional surrender of the Imperial Japanese Armed Forces in the Potsdam Declaration on 26 July 1945, the alternative being "prompt and utter destruction". The Japanese government ignored the ultimatum.

A learning curve is a graphical representation of the relationship between how proficient people are at a task and the amount of experience they have. Proficiency (measured on the vertical axis) usually increases with increased experience (the horizontal axis), that is to say, the more someone, groups, companies or industries perform a task, the better their performance at the task.

The common expression "a steep learning curve" is a misnomer suggesting that an activity is difficult to learn and that expending much effort does not increase proficiency by much, although a learning curve with a steep start actually represents rapid progress. In fact, the gradient of the curve has nothing to do with the overall difficulty of an activity, but expresses the expected rate of change of learning speed over time. An activity that it is easy to learn the basics of, but difficult to gain proficiency in, may be described as having "a steep learning curve".

"Fat Man" (also known as Mark III) was the design of the nuclear weapon the United States used for seven of the first eight nuclear weapons ever detonated in history. It is also the most powerful design to ever be used in warfare.

A Fat Man device was detonated over the Japanese city of Nagasaki on 9 August 1945. It was the second and larger of the only two nuclear weapons ever used in warfare. It was dropped from the Boeing B-29 Superfortress Bockscar piloted by Major Charles Sweeney. Its detonation marked the third nuclear explosion in history. The name Fat Man refers to the wide, round shape. Fat Man was an implosion-type nuclear weapon with a solid plutonium core, and later with improved cores.

During the Pacific War, Allied forces conducted air raids on Japan from 1942 to 1945, causing extensive destruction to the country's cities and killing between 241,000 and 900,000 people. During the first years of the Pacific War these attacks were limited to the Doolittle Raid in April 1942 and small-scale raids on Japanese military positions in the Kuril Islands from mid-1943. Strategic bombing raids began in June 1944 and continued with increasing intensity until the end of the war in August 1945. Allied naval and land-based tactical air units also attacked Japan during 1945.

The United States Army Air Forces (USAAF) campaign against Japan began in earnest in mid-1944 and intensified during the final months of the war. While plans for attacks on the Japanese home islands had been prepared prior to the Pacific War, these could not begin until the long-range Boeing B-29 Superfortress bomber was ready for combat and in production at scale. From June 1944 until January 1945, B-29s stationed in India and staged through bases in China made a series of nine raids on targets in western Japan, but this effort proved ineffective. The strategic bombing campaign was greatly expanded from November 1944, when airfields in the Mariana Islands became available as a result of the Mariana Islands Campaign. Initial attempts to target industrial facilities using high-altitude daylight "precision" bombing were ineffective in significantly degrading Japanese war economy, due to a mix of poor weather conditions, Japanese air defenses, and the jet stream impeding accuracy.

Little Boy was a type of atomic bomb created by the Manhattan Project during World War II. The name is also often used to describe the specific bomb (L-11) used in the bombing of the Japanese city of Hiroshima by the Boeing B-29 Superfortress Enola Gay on 6 August 1945, making it the first nuclear weapon used in warfare, and the second nuclear explosion in history, after the Trinity nuclear test. It exploded with an energy of approximately 15 kilotons of TNT (63 TJ) and had an explosion radius of approximately 1.3 kilometres (0.81 mi) which caused widespread death across the city. It was a gun-type fission weapon which used uranium that had been enriched in the isotope uranium-235 to power its explosive reaction.

Little Boy was developed by Lieutenant Commander Francis Birch's group at the Los Alamos Laboratory. It was the successor to a plutonium-fueled gun-type fission design, Thin Man, which was abandoned in 1944 after technical difficulties were discovered. Little Boy used a charge of cordite to fire a hollow cylinder (the "bullet") of highly enriched uranium through an artillery gun barrel into a solid cylinder (the "target") of the same material. The design was highly inefficient: the weapon used on Hiroshima contained 64 kilograms (141 lb) of uranium, but less than a kilogram underwent nuclear fission. Unlike the implosion design developed for the Trinity test and the Fat Man bomb design that was used against Nagasaki, which required sophisticated coordination of shaped explosive charges, the simpler but inefficient gun-type design was considered almost certain to work, and was never tested prior to its use at Hiroshima.

Heavy bombers are bomber aircraft capable of delivering the largest payload of air-to-ground weaponry (usually bombs) and longest range (takeoff to landing) of their era. Archetypal heavy bombers have therefore usually been among the largest and most powerful military aircraft at any point in time. In the second half of the 20th century, heavy bombers were largely superseded by strategic bombers, which were often even larger in size, had much longer ranges and were capable of delivering nuclear bombs.

Because of advances in aircraft design and engineering — especially in powerplants and aerodynamics — the size of payloads carried by heavy bombers has increased at rates greater than increases in the size of their airframes. The largest bombers of World War I, the Riesenflugzeuge of Germany, could carry a payload of up to 4,400 pounds (2,000 kg) of bombs; by the latter half of World War II, the Avro Lancaster (introduced in 1942) routinely delivered payloads of 14,000 pounds (6,400 kg) (and sometimes up to 22,000 lb (10,000 kg)) and had a range of 2,530 miles (4,070 km), while the B-29 (1944) delivered payloads in excess of 20,000 pounds (9,100 kg) and had a range of 3,250 miles (5,230 km). By the late 1950s, the jet-powered Boeing B-52 Stratofortress, travelling at speeds of up to 650 miles per hour (1,050 km/h) (more than double that of a Lancaster), could deliver a payload of 70,000 pounds (32,000 kg), over a combat radius of 4,480 miles (7,210 km).

Bockscar, sometimes called Bock's Car, is the United States Army Air Forces Boeing B-29 Superfortress bomber that dropped a Fat Man atomic bomb over the Japanese city of Nagasaki during World War II in the second – and most recent – nuclear attack in history. One of 15 Silverplate B-29s used by the 509th, Bockscar was built at the Glenn L. Martin Bomber Plant at Bellevue, Nebraska, at what is now Offutt Air Force Base, and delivered to the United States Army Air Forces on 19 March 1945. It was assigned to the 393rd Bombardment Squadron, 509th Composite Group to Wendover Army Air Field, Utah, in April and was named after captain Frederick C. Bock.

Bockscar was used in 13 training and practice missions from Tinian, and three combat missions in which it dropped pumpkin bombs on industrial targets in Japan. On 9 August 1945, Bockscar, piloted by the 393rd Bombardment Squadron's commander, Major Charles W. Sweeney, dropped a Fat Man nuclear bomb with a blast yield equivalent to 21 kilotonnes of TNT (88 TJ) over the city of Nagasaki. The explosion destroyed about 44% of the city, killed 35,000 people, and injured 60,000 people.