Operation Grapple - Explosions

Explosions

The first trial was Grapple, also known as Grapple 1. All of these nuclear bombs were dropped and detonated over Malden Island. The first test of this trial was code-named Short Granite. It was a two-staged nuclear weapon that had a predicted yield of about one megaton. This bomb was dropped by a Vickers Valiant bomber XD818, piloted by Kenneth Hubbard, off the shore of Malden Island on 15 May 1957.

Weighing about 4,550 kilograms, this bomb exploded with a power of about 300 kilotons, a nuclear weapon yield far below its designed capability. Despite this problem, the British government hailed this test as a successful thermonuclear explosion, and the government announced to the world that the U.K. had become a thermonuclear power. While the results of this test were disappointing, the British learned much about radiation implosion in H-bombs.

The next test was Orange Herald. This was a large fission bomb which was hoped to arm a future ballistic missile. The bomb was dropped and detonated by a Valiant bomber on May 31, 1957. It exploded with a force of about 720 kilotons. The yield was the largest ever achieved by similar bomb designs. This bomb was hailed by the government as a new type of hydrogen bomb and the fact that it was a fission bomb was kept secret by the government until the end of the Cold War. A 400 kiloton very-large atomic bomb code-named "Green Grass" was derived from Orange Herald, and it was deployed during the period before an actual H-bomb became available.

The last shot of Grapple was Purple Granite. This was a last minute addition to the operation and was hoped to give an improved yield over Short Granite. The bomb was detonated on June 19, 1957, with a 200 kiloton yield.

There were other designs that were not tested: Green Bamboo was a single stage thermonuclear bomb similar to the Soviet Joe-4, and Orange Herald (large) was a "political bomb": a large fission bomb that was not suitable for use as a weapon but was certain to give a high yield ensuring that Britain would not appear as a failed nuclear power.

The two Granites and Green Bamboo were designed to achieve high yields by using the Li-6 D/U-238 cycle rather than the large-scale fusion of deuterium achieved at Grapple-Y.