Red Snow was a British thermonuclear weapon, based on the US W28 (then called Mark 28) design used in the B28 thermonuclear bomb and AGM-28 Hound Dog missile. The US W28 had yields of 70, 350, 1,100 and 1,450 kilotonnes of TNT (0.29, 1.46, 4.60 and 6.07 PJ) and while Red Snow yields are still classified, declassified British documents indicate the existence of "kiloton Red Snow" and "megaton Red Snow" variants of the weapon, suggesting similar yield options, while other sources have suggested a yield of approximately 1 megatonne of TNT (4.2 PJ).
The Red Snow warhead was developed after a September 1958 decision to adopt the US warhead for British use, following the 1958 US-UK Mutual Defence Agreement. It entered service in 1961, remaining in use until 1972, when it was replaced by the WE.177 bomb. Production numbers are classified, but it is believed that less than 150 weapons were produced.
Red Snow was used as both a free-fall bomb and as the warhead of the Blue Steel missile. In the gravity bomb role, it was fitted into the casing of the Yellow Sun weapon, even though the Red Snow warhead was considerably smaller than that of the original Yellow Sun bomb.
The Red Snow physics package was later reduced in size, weight and yield, and fitted with a smaller more modern primary, intended as a Red Beard replacement. Known as Una, this was later reduced in diameter and renamed Ulysses as the physics package intended for the UK warhead on the Skybolt project.
Red Snow used the primary stage Peter, an anglicised version of the US Python device used in the W28. The Peter device contained 2.25 kilograms (5.0 lb) of plutonium and 1.4 kilograms (3.1 lb) of uranium. The kiloton Red Snow contained 1.6 kilograms (3.5 lb) of plutonium, 11 kilograms (24 lb) of uranium, 0.6 kilograms (1.3 lb) of lithium deuteride and 2.49 to 2.54 grams (0.088 to 0.090 oz) of tritium, while in megaton Red Snow all the values stayed the same except the lithium deuteride amount which increased to 16 kilograms (35 lb).
The device was fitted inside weapon cases from the older Yellow Sun weapons. This may have been to simplify crew retraining, simplify integration of the new weapon to existing platforms, or to hide the radical reduction in weapon size.
- "Yellow Sun MK.2 Enters Service". Atomic Weapons Establishment. September 2007. Archived from the original on 7 June 2007.
- "Defence Committee on Nuclear Requirements 1959–1963". Atomic Weapons Research Establishment. National Archive. 17 July 1962. p. 1. TNA AVIA 65/1771 E24. Archived from the original on 28 May 2012. Retrieved 2 January 2012.
Red Snow is the British version of the U.S. Mk.28, which has been tested by the American Authorities. It follows that all current British nuclear weapons are based on tested designs.
- Sublette, Carey (12 June 2020). "Complete List of All U.S. Nuclear Weapons". Nuclear weapon archive. Archived from the original on 27 February 2009. Retrieved 18 March 2021.
- Weapons Department Atomic Warheads Production Committee, Papers & Minutes (Report). UK Atomic Energy Authority. 1964. p. 63. TNA AB 16/4675. Archived from the original on 23 May 2021. Retrieved 27 April 2022.
- Burnell, Brian (15 April 2018). "WE.177". Nuclear Weapons: a Guide to British Nuclear Weapon Projects. Archived from the original on 27 September 2018. Retrieved 3 May 2022.
PETER – A boosted fission device, an anglicised copy of the W-34 Python primary used in the Red Snow strategic warhead and it was already in production in the UK, so could be available quickly. Yield of 11 kt was not capable of enlargement to the sizes specified by OR.1176 / 1177.
- Sublette, Carey (30 April 2002). "History of the British Nuclear Arsenal". Nuclear Weapon Archive. Retrieved 3 May 2022.
- Blue Steel Nuclear Missile Enters Service, Atomic Weapons Establishment timeline, September 2007
- "Nuclear-weapons.info". Archived from the original on 27 September 2018. Retrieved 8 November 2009.