Britain detonates its first hydrogen bomb in the Pacific
On this day · 15 May 1957
A Valiant bomber dropped Britain's first thermonuclear weapon over the Pacific, vaulting the nation into the H-bomb club.
On May 15, 1957, a Royal Air Force Vickers Valiant bomber, flown by Wing Commander Kenneth Hubbard, released Britain’s first hydrogen bomb high over Malden Island in the central Pacific. Code-named Short Granite, the device fell from around 14,000 metres and burst above the sea as part of Operation Grapple, staged from a base on Christmas Island.
The test was hailed as a triumph that made the United Kingdom the third nation, after the United States and Soviet Union, to wield thermonuclear weapons.
The bomb yielded roughly 300 kilotons—only about a quarter of its one-megaton design—a shortfall quietly kept secret until 1993.
Even so, the demonstration served its purpose. It strengthened Britain’s hand and helped restore nuclear cooperation with Washington through the 1958 US–UK Mutual Defence Agreement. Later Grapple tests achieved true megaton yields, cementing the country’s place among the thermonuclear powers.
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