Yellow Sun
|
|
Yellow Sun was the first operational British thermonuclear weapon, with a yield of about 1 megaton. The name actually refers only to the outer casing, the physics package inside was known as Green Grass or Red Snow, and the neutron source (tritium capsule) was Blue Stone. It was some 21 feet (6.4 meters) long, and quite heavy at about 7,250lb. It featured a flat nose instead of a more rounded bomb profile, in order to allow it to fit into the bomb bays of the V bomber fleet.
Yellow Sun was being built while testing of the fusion physics package was still taking place. For this reason the first Yellow Sun Mk.1 was built using the Green Grass boosted fission device of about 400kT, which had originally been placed in the larger and heavier Blue Danube casings of the UK's first nuclear weapons to produce Violet Club. It appears that the Green Grass warhead was never tested, although there is reason to suspect that it was very similar to the Green Bamboo device tested during the Operation Grapple series of tests in 1957.
Deployment on the V bomber fleet started in 1958. It is thought that these bombs were intended as "emergency" weapons, and had not been engineered for reliable long-term stockpiling. It was carried (briefly) by the RAF's V bomber force. Production halted in September 1958, when the decision was made to adopt the physics package of the American W28 warhead (used in the B28 nuclear bomb) instead.
Red Snow was both more powerful and much smaller than Green Grass. Nevertheless the new physics package was placed in the existing design to produce Yellow Sun Mk.2, likely in order to reduce crew training and testing cycles. Yellow Sun Mk. 2 entered service in 1961, and remained the primary air-dropped strategic weapon until replaced with the WE.177.