On the 15th May 1957 Britain dropped its first H-bomb.
From the BBC:
Britain exploded its first hydrogen bomb test at high altitude over the largely uninhabited Malden Island to minimise nuclear fall-out. Malden Island, located about 365 miles southwest of Christmas Island [also called Kiritimati], was the site for the bomb dropping tests, with Christmas Island being the base for operations.
The bomb by a unit from No 49 Squadron RAF Bomber Command, normally based at RAF Wittering, Northants.
This first bomb was code named: Short Granite.
All bombs were dropped over or near Malden Island
The island is now a protected area for breeding seabirds.
Kiritimati [Christmas Island] is a part of the Republic of Kiribati, which became independent from the United Kingdom in 1979, and is member of the Commonwealth of Nations, the IMF and the World Bank, and became a full member of the United Nations in 1999.
During the Cold War there was some nuclear weapons testing in the Christmas Island area.
The United Kingdom supposedly conducted its first successful hydrogen bomb test at Malden Island on 15 May 1957; Christmas Island was the operation’s main base.
In fact, this test did not work as planned, and the first British H-bomb was successfully detonated over the southeastern tip of Christmas Island on 8 November 1957.
Subsequent test series in 1958 (Grapple Y and Z) took place above or near Christmas Island itself.
The United States conducted 22 successful nuclear detonations as part of Operation Dominic here in 1962. Some toponyms (like Banana and Main Camp) come from the nuclear testing period, during which at times over 4,000 servicemen were present.
By 1969, military interest in Christmas Island had ceased and the facilities were abandoned and for the most part dismantled. Some communications, transport and logistics facilities, however, were converted for civilian use and it is due to these installations that Christmas Island came to serve as the administrative center for the Line Islands.
The United Kingdom detonated some 5 megatonnes of TNT (21 PJ) of nuclear payload near and 1.8 megatonnes of TNT (7.5 PJ) directly above Christmas Island in 1957/58, while the total yield of weapons tested by the United States in the vicinity of the island between 25 April and 11 July 1962 was 24-megatonne-of-TNT (100 PJ).
During the British Grapple X test of 8 November 1957 which took place directly above the southeastern tip of Christmas Island, yield was stronger than expected and there was some blast damage in the settlements.
Islanders were usually not evacuated during the nuclear weapons testing, and data on the environmental and public health impact of these tests remains contested.
114.1 - 764,679