Deployment
Deployment started in 1959-60. Yellow Sun Mk.1 was intended as an "emergency" weapon, and had not been engineered for reliable long-term stockpiling. It was always envisaged that a Mk.2 version would be available later fitted with a true thermonuclear warhead derived from the Granite type tested at Grapple, or an American type made available after the 1958 Anglo-US Bilateral Agreement. It was carried only by RAF V bombers. In September 1958 a decision was made to abandon the Granite type warheads intended for Yellow Sun Mk.2 (and Blue Steel, and Blue Streak MRBM) and instead adopt the US W-28 warhead used in the US Mk-28 nuclear bomb. This was anglicised to adapt it to British engineering practices, and manufactured in Britain using British fissile materials and known as Red Snow.
Red Snow was both more powerful, lighter and smaller than Green Grass. It was always envisaged that the Yellow Sun bomb casing would be adapted for successor warheads to minimise unessential development time and cost. Yellow Sun Mk. 2 entered service in 1961, and remained the primary air-dropped strategic weapon until replaced with WE.177B in 1966.
Although the first British designed thermonuclear weapon to be deployed, Yellow Sun was not the first to be deployed with the RAF. US Mk-28 and Mk-43 thermonuclear bombs and others had been supplied to the RAF for use in V bombers prior to the deployment of Yellow Sun. Some bombers of the V-force only ever used American weapons supplied under dual-key arrangements.
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