Glossary

A to Z

509th Composite Group

The self-contained Army Air Forces unit formed to drop the atomic bombs. It was activated at Wendover, Utah, on 17 December 1944 under Lieutenant Colonel Paul Tibbets, and had 225 officers and 1,542 enlisted men.^{Sources: 1, 2, 3} See The plane, The crews.

Alsos

The Allied mission that followed the German atomic programme across Europe. It was set up in the autumn of 1943, commanded by Boris Pash, with Samuel Goudsmit leading the scientists.^{Sources: 4} See The German bomb.

Bockscar

The B-29 that dropped Fat Man on Nagasaki. It was named after Captain Frederick Bock, its usual commander, and the name was painted on after the mission.^{Sources: 5, 6} See The plane, The crews.

Calutron

A machine that separated uranium-235 from ordinary uranium by its weight, at Y-12 in Oak Ridge. About 10,000 young women ran the calutrons, and learned what they had been making on 6 August 1945.^{Sources: 7, 8} See The bomb.

Circle R

The tail marking of the 6th Bomb Group, painted on Enola Gay so that it would look like an ordinary bomber. The 509th’s own marking was an arrow in a circle.^{Sources: 9, 10, 11} See The plane.

Enola Gay

The B-29 that dropped Little Boy on Hiroshima. Tibbets named it after his mother, Enola Gay Tibbets, and the name was painted on the day before the mission.^{Sources: 9, 12} See The plane, The crews.

Farm Hall

A country house at Godmanchester, in England, where ten German nuclear scientists, among them Heisenberg, Hahn, von Weizsäcker and Diebner, were held from 3 July 1945 to 3 January 1946. Their conversations were secretly recorded.^{Sources: 13, 14, 15} See The German bomb.

Fat Man

The bomb dropped on Nagasaki. It was an implosion bomb with a plutonium core of about 6.2 kg, the same design as the Trinity device. Its yield was about 21 kilotons, uncertain by about 10 per cent.^{Sources: 16, 17, 18, 19, 20} See The bomb.

Gun-type bomb

A design in which one piece of uranium is fired down a barrel into another, so that together they start a chain reaction. Little Boy was a gun-type bomb.^{Sources: 21, 22} See The bomb.

Hibakusha

The Japanese word for the survivors of the two bombs. It means atomic bomb affected people.^{Sources: 23} See The cost.

Hypocentre

The point on the ground directly below where a bomb exploded. In Nagasaki a black granite monument marks it, about 500 metres below the burst at 11:02, and the register of the dead is kept in front of it on microfilm.^{Sources: 24, 25} See Visit.

Implosion

A design in which explosives squeeze a ball of plutonium until it starts a chain reaction. Plutonium from the reactors proved unsuitable for a gun design, so in July 1944 Los Alamos switched to implosion.^{Sources: 26} See The bomb.

Interim Committee

The committee of officials and scientists that advised on the bomb in 1945. On 1 June 1945 it advised using it without prior warning.^{Sources: 27} See The decision and the debate.

Kiloton

A measure of explosive power, equal to a thousand tons of TNT. Little Boy’s yield was about 15 kilotons, uncertain by about 20 per cent, and Fat Man’s about 21 kilotons, uncertain by about 10 per cent.^{Sources: 16, 20, 21} See The bomb.

Lesart

German for a version or reading. It became the name, from Max von Laue, for the claim that the German scientists could have built a bomb but chose not to.^{Sources: 15, 28} See The German bomb.

Little Boy

The bomb dropped on Hiroshima. It was a gun-type bomb holding about 64 kg of highly enriched uranium, and it was never tested, because a test would have used all the uranium-235 there was. Its yield was about 15 kilotons, uncertain by about 20 per cent.^{Sources: 17, 20, 21, 22, 29} See The bomb.

Loading pit

The bombs were too large to wheel under a B-29, so two pits with hydraulic lifts were dug on Tinian, and a third on Iwo Jima. The bomb was lowered into the pit on a trailer, the aircraft was edged backwards over it, and the bomb was raised into the bomb bay.^{Sources: 3, 30, 31, 32} See Tinian.

Manhattan Engineer District

The Army organisation that ran the American atomic bomb project, set up on 13 August 1942; the Manhattan Project is its everyday name. Engineer districts were named after the city where they began, and this one began at 270 Broadway, Manhattan.^{Sources: 33, 34, 35, 36} See The bomb.

MAUD Committee

The British committee of scientists that concluded in July 1941 that a uranium bomb could be built in about two years.^{Sources: 37, 38} See Britain and the bomb, The bomb.

McMahon Act

The Atomic Energy Act of 1946, signed on 1 August 1946, which ended the sharing of atomic information with other countries, Britain included.^{Sources: 39, 40, 41} See After 1945.

North Field

The airfield at the north end of Tinian, in 1945 the largest airfield in the world. Project Alberta and the 509th Composite Group met there.^{Sources: 3, 30, 42} See Tinian.

Potsdam Declaration

The warning issued to Japan on 26 July 1945 in the names of the United States, Britain and China, demanding unconditional surrender and threatening prompt and utter destruction.^{Sources: 43, 44} See The cost.

Project Alberta

The Los Alamos team that assembled the bombs on Tinian and armed them in flight. It was set up in March 1945. Fifty-one of its members went to Tinian.^{Sources: 3, 45, 46, 47} See Project Alberta, The bomb, Tinian.

Pumpkin bomb

A practice bomb the same shape and weight as Fat Man. At Wendover the 509th dropped pumpkins, mostly filled with concrete, aiming to land within 200 feet from 30,000 feet. From 20 July 1945, filled with explosive, they were dropped on targets in Japan.^{Sources: 1, 48, 49, 50} See The plane.

Silverplate

The code name for the B-29s modified to carry atomic bombs; the work began as the Silver Plated Project. The 509th took 15 Silverplate B-29s to Tinian, all built by Martin at Omaha.^{Sources: 12, 51, 52, 53} See The plane.

Trinity

The first test of an atomic bomb, on 16 July 1945, on a 100-foot (30 m) steel tower in the Jornada del Muerto, now White Sands Missile Range, in New Mexico.^{Sources: 19, 54, 55} See The bomb.

Uranverein

The “Uranium Club”, Germany’s nuclear research programme. Kurt Diebner of the Army Ordnance Office held its first meeting on 16 September 1939, and Heisenberg was brought in for the theory of chain reactions.^{Sources: 56, 57, 58} See The German bomb.

Victor number

The number painted on each 509th aircraft for the missions. Enola Gay carried 82 and Bockscar 77.^{Sources: 9, 53, 59, 60} See The plane.

Weaponeer

The officer who looked after the bomb in flight. On each strike aircraft the weaponeer came from Project Alberta and his assistant from the 1st Ordnance Squadron. On the way to Hiroshima, Parsons loaded Little Boy’s propellant charges in flight, so that a crash on take-off could not set it off.^{Sources: 46, 47, 61, 62, 63} See The crews.