Blue Danube (nuclear weapon)

Blue Danube was the first operational British nuclear weapon. It also went by a variety of other names, including Smallboy, the Mk.1 Atom Bomb, Special Bomb and OR.1001, a reference to the Operational Requirement it was built to fill.

The RAF V bomber force was initially meant to use Blue Danube as their primary armament at a time when the first hydrogen bomb had not been detonated, and the British military planners still believed that an atomic war could be fought and won using atomic bombs of similar yield to the Hiroshima bomb. For that reason the stockpile planned was for up to 800 bombs with yields of approx. 10-12 kilotons. V-bomber bomb bays were sized to carry Blue Danube, the smallest-size nuclear bomb that was possible to be designed given the technology of the day (1947) when their plans were formulated.

Initial designs for the Blue Danube warhead were based on research derived from Hurricane, the first British fission device (which was not designed nor employed as a weapon), tested in 1952. The actual Blue Danube warhead was proof-tested at the Marcoo (surface) and Kite (air-drop) nuclear trials sites in Maralinga, Australia, by a team of Australian, British and Canadian scientists in late 1956.

Blue Danube added a ballistically shaped casing to the existing Hurricane physics package, with four flip-out fins to ensure a stable ballistic trajectory from the planned release height of 50,000 ft. It initially used a plutonium core, but all service versions were modified to use a composite plutonium/U-235 core, and a version was also tested with a uranium-only core. The service chiefs insisted on a yield of between 10-12 kt for two reasons: firstly, to minimise usage of scarce and expensive fissile material; and secondly, to minimise the risk of predetonation, a phenomenon then little understood, and the primary reason for using a composite core of concentric shells of plutonium and U-235. Although there were many plans for versions with higher yields, some up to 40 kt, none were developed, largely because of the scarcity of fissile materials, and there is no evidence that any were seriously contemplated.

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