Operation Grapple was a United Kingdom tri-service exercise leading to the detonation of the first British hydrogen bomb on May 15, 1957.

The operation centred on Christmas Atoll (now Kiritimati) in the mid-Pacific. There were both air bursts in the Pacific and also low level tests carried out at Maralinga, South Australia. There were nine open-air nuclear tests in all, conducted from May 1957 to September 1958. Both fission and fusion weapons were tested.

The very first fusion device was dropped from Vickers Valiant XD818 [1], piloted by Kenneth Hubbard , over Malden Island. The bomb weighed around 4,545 kg, code-named Green Granite or Short Granite, it was a combination fission-fusion device with a Red Beard primary and a lithium deuteride secondary. The expected yield was around 1 megaton.

It was released from a height of almost 13 km and exploded at 19:37 GMT after almost a minute in free-fall at 2,438 m (8,000 ft) above the ground. The device yielded just 300 kilotons. The relatively low yield prompted a redesign of the later bombs, the first test to yield over a megaton was on November 8 (Grapple X, bomb Round C). The final air burst tests on September 2 and 11, 1958 dropped bombs that yielded almost 3 megatons - Britain's most powerful tests.

The operation was initiated by the arrival of the advanced party of troops at the end of May 1956, building up to around 1200 civilian and military participants at the end of that year. Initial landings were from the Bibby Line troopship 'Devonshire' which had sailed from the Far East and embarked servicemen at Suva (Fiji) who had been flown from Britain by commercial airlines. From early October, following the rebuilding of the island's main runway, the majority of arrivals came directly from Britain, via Hawaii, using Qantas chartered 'Super Constellation' aircraft. Departures of the first arrivals started early June 1957, using the same Qantas arrangement to Hawaii.

While Christmas was the main base, three other locations featured as key elements of the operation. Malden Island, about 200 miles south of 'Christmas' was the site for the air-dropped tests, and Penrhyn Island, a further 200 miles south was used as a monitoring site and weather station. Air support for the operation was generally routed through Hickmam air base on the Hawaiian Islands to the north, where a support group was located.

Supplies for the island were shipped primarily from the southern hemisphere - Australia and New Zealand, by freighters of the Royal Fleet Auxillary (RFA). The Royal Navy established a water processing plant early in the operation, which provided adequate supplies of drinking water and semi-salt water for showering.

Followed by Operation Antler.

External links

• Valiant XD818 is preserved at the RAF Museum