Grapple X (Round C)

Test deviceUnited KingdomThermonuclear (staged)

No freely licensed photo of this device yet.

Yield · TNT equivalent1.8 Mt

Key specs

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

Overview

Britain’s first fully successful hydrogen bomb test, air-dropped off Christmas Island in November 1957. At 1.8 Mt it exceeded predictions, although most of its energy still came from fission.

Effect radii: estimates

Calculated for 1.8 Mt

Fireball, maximum radius: ≈ 1.2 km
Initial radiation, 500 rem (5 Sv): ≈ 3.5 km
Blast 5 psi: most buildings collapse: ≈ 8.6 km
Thermal: third-degree burns: ≈ 14 km
Blast 1 psi: windows shatter: ≈ 27 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
Nov 8, 1957	Grapple X	Christmas Island (Kiritimati), Pacific Ocean	1.8 Mt

Sources

Operation Grapple, Wikipedia