Orange Herald

Test deviceUnited KingdomLayered fission–fusion

No freely licensed photo of this device yet.

Yield · TNT equivalent720 kt

Key specs

Country: United Kingdom
Design: Layered fission–fusion
Type: Test device
Number built: 1

Overview

A very large boosted-fission device dropped over Malden Island in May 1957. At 720 kt it remains the largest fission explosion ever achieved, but it was not a true hydrogen bomb.

Effect radii: estimates

Calculated for 720 kt

Fireball, maximum radius: ≈ 850 m
Initial radiation, 500 rem (5 Sv): ≈ 2.9 km
Blast 5 psi: most buildings collapse: ≈ 6.4 km
Thermal: third-degree burns: ≈ 9.9 km
Blast 1 psi: windows shatter: ≈ 20 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 31, 1957	Grapple 2 (Orange Herald)	Malden Island, Pacific Ocean	720 kt

Sources

Operation Grapple, Wikipedia