Red Snow was a British

United Kingdom

The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...

 thermonuclear weapon. Its physics package was apparently similar, if not identical, to that of the United States

United States

The United States of America is a federal constitutional republic comprising fifty states and a federal district...

 W28 nuclear warhead used in the B28 nuclear bomb

B28 nuclear bomb

The B28, originally Mark 28, was a thermonuclear bomb carried by U.S. tactical fighter bombers and bomber aircraft. From 1962 to 1972 under the NATO nuclear weapons sharing program, American B28s also equipped six Europe-based Canadian CF-104 squadrons known as the RCAF Nuclear Strike Force...

 and AGM-28 Hound Dog

AGM-28 Hound Dog

The North American Aviation Corporation AGM-28 Hound Dog was a supersonic, jet propelled, air-launched cruise missile. The Hound Dog missile was first given the designation B-77, then redesignated the GAM-77, and finally designated the AGM-28, permanently...

 missile, with an explosive yield of approximately 1.1 megaton

TNT equivalent

TNT equivalent is a method of quantifying the energy released in explosions. The ton of TNT is a unit of energy equal to 4.184 gigajoules, which is approximately the amount of energy released in the detonation of one ton of TNT...

.

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

1958 US-UK Mutual Defence Agreement

The 1958 US–UK Mutual Defence Agreement is a bilateral treaty between the United States and the United Kingdom on nuclear weapons cooperation.It was signed after the UK successfully tested its first hydrogen bomb during Operation Grapple. While the U.S...

. It entered service in 1961, remaining in use until 1972, when it was replaced by the WE.177

WE.177

WE.177 was the last air-delivered tactical nuclear weapon of the British Armed Forces. There were three versions; WE.177A was a boosted fission weapon, while WE.177B and WE.177C were thermonuclear weapons...

 bomb. Perhaps 150 were produced.

Red Snow was used as both a free-fall bomb and as the warhead of the Blue Steel missile

Blue Steel missile

The Avro Blue Steel was a British air-launched, rocket-propelled nuclear stand-off missile, built to arm the V bomber force. It was the primary British nuclear deterrent weapon until the Royal Navy started operating Polaris missile armed nuclear submarines....

. In the gravity bomb role, it was fitted into the casing of the Yellow Sun

Yellow Sun

Yellow Sun was the first British operational high-yield strategic nuclear weapon. The name actually refers only to the outer casing; the warhead was known as "Green Grass" and "Red Snow"...

 weapon, even though the Red Snow warhead was considerably smaller than that of the original Yellow Sun bomb.

The Red Snow warhead was later reduced in size, weight and yield, and fitted with a smaller more modern primary, intended as a Red Beard

Red Beard (nuclear weapon)

Red Beard was the first British tactical nuclear weapon. It was carried by the English Electric Canberra and the V bombers of the Royal Air Force, and by the Blackburn Buccaneers, Sea Vixens and Supermarine Scimitars of the Royal Navy's Fleet Air Arm...

 replacement. Known as Una, this was later reduced in diameter and renamed Ulysses as the warhead intended for the UK warhead for the Skybolt project.