The Yellow Sun Mk.1 nuclear bomb was the first high-yield bomb that Britain developed. Its development was very fast, and was built as an “emergency weapon” after the Grapple nuclear tests carried out in 1957 in Malden Island, Republic of Kiribati. This bomb used radiation implosion technology and was the first real British H-bomb. Its warhead was called Green Grass, had a yield of 400kt and consisted of a pure fission device with 70kg of fissile material developed from the previous Green Bamboo device. It was considered a very dangerous system and the core of the system was surrounded by 133,000 steel ball-bearings to avoid accidental crushing of the core, This protection had to be removed in case the bomb had to be used. The technology of this project was defined as “little advanced and unproven”, and that was due to the urgency of the moment and the need to have this type of weapons in a quick way by the fear of a Soviet attack. It entered service in 1958, but in September of that same year, Great Britain decided to use the American Mk.28 thermonuclear bomb and the production of the Yellow Sun Mk.1 was stopped after 37 units built.

YELLOW SUN Mk.1 gallery and more info


Información adicional

Ficha Completa
Country of origin

United Kingdom


Nuclear bomb

Entered service


Missile/bomb dimensions, (length x diameter)

6.40 x 1.20 meters

Missile/bomb weight

3,290 kg

Warhead, (explosive charge)

Weight: 70 kg – Fissile material: Uranium – Type: Green Grass fission device

Yield, (maximum)

400 Kilotons