Short Granite

Test deviceUnited KingdomThermonuclear (staged)

No freely licensed photo of this device yet.

Yield · TNT equivalent300 kt

Key specs

Country: United Kingdom
Design: Thermonuclear (staged)
Type: Test device
Number built: 1

Overview

Britain’s first attempt at a hydrogen bomb, dropped from a Valiant over Malden Island in May 1957 in Operation Grapple. It yielded 300 kt, far below what was hoped for.

Effect radii: estimates

Calculated for 300 kt

Fireball, maximum radius: ≈ 600 m
Initial radiation, 500 rem (5 Sv): ≈ 2.5 km
Blast 5 psi: most buildings collapse: ≈ 4.8 km
Thermal: third-degree burns: ≈ 6.9 km
Blast 1 psi: windows shatter: ≈ 15 km

Estimated ground ranges for an air burst at the optimum height over flat, open ground, computed from the yield with standard scaling laws. These are not measurements: real effects depend on the height of burst, terrain, buildings and weather.

Formulas from: Glasstone & Dolan, The Effects of Nuclear Weapons (1977), chapter II; Carey Sublette, Nuclear Weapons FAQ, section 5

Tests and use

Date	Event	Site	Yield
May 15, 1957	Grapple 1 (Short Granite)	Malden Island, Pacific Ocean	300 kt

Sources

Operation Grapple, Wikipedia