Yellow Sun (nuclear weapon)

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Yellow Sun
A Yellow Sun at the Royal Air Force Museum Cosford (2011)
Type	Nuclear weapon
Place of origin	United Kingdom
Specifications
Mass	7,250 pounds (3,290 kg)
Length	21 feet (6.4 m)
Diameter	4 feet (1.2 m)
Filling	Uranium – Green Grass warhead Plutonium/Hydrogen – Red Snow warhead
Blast yield	400 kt (1,700 TJ) Green Grass warhead 1.1 Mt (4.6 PJ) Red Snow warhead

Yellow Sun was the first British operational high-yield strategic nuclear weapon warhead. The name refers only to the outer casing; the warhead (or physics package) was known as "Green Grass" in Yellow Sun Mk.1 and "Red Snow" (a US design) in Yellow Sun Mk.2.

Yellow Sun was designed to contain a variety of warheads. The initial plan was that it would carry an alarm-clock-type warhead known as "Green Bamboo", and then replace it with a true thermonuclear warhead known as "Green Granite". After signing a weapon technology agreement with the US, both concepts were dropped. Green Granite would be replaced by Red Snow at an earlier service date. This meant the interim Green Bamboo was less important and it was replaced by the less powerful and simpler "Green Grass".

A unique feature of the Yellow Sun casing was its completely flat nose. This provided two benefits, one was that the drag allowed the bomb to fall behind the bomber a safe distance before detonation, and the other was that it did not generate the complex pattern of shock waves that a classically curved nose created, which made it difficult to measure altitude barometrically.

Mark 1 with Green Grass began to enter service in 1959, replacing the massive Blue Danube over the next year. Mark 2 with Red Snow began to replace it in 1961. Beginning in 1966, Yellow Sun was replaced by the WE.177, based on another US design.