Grapple Y

Test deviceUnited KingdomThermonuclear (staged)

No freely licensed photo of this device yet.

Yield · TNT equivalent3 Mt

Key specs

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

Overview

The largest British nuclear test, about 3 Mt, dropped off Christmas Island in April 1958. A true two-stage hydrogen bomb with most of its yield from fusion, it helped lead to the 1958 US–UK Mutual Defence Agreement.

Effect radii: estimates

Calculated for 3 Mt

Fireball, maximum radius: ≈ 1.5 km
Initial radiation, 500 rem (5 Sv): ≈ 3.8 km
Blast 5 psi: most buildings collapse: ≈ 10 km
Thermal: third-degree burns: ≈ 18 km
Blast 1 psi: windows shatter: ≈ 32 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
Apr 28, 1958	Grapple Y	Christmas Island (Kiritimati), Pacific Ocean	3 Mt

Sources

Operation Grapple, Wikipedia

Grapple Y · Armory Atlas