Opperation Grapple was a series of tests carried out by the UK to develop a working Thermonuclear bomb, more commenly known as a H-Bomb.
Previous nuclear bomb tests that the UK had carried out, had been in Australia, but because of the issues of contamination caused by these tests etc., and the fact that the H-bombs were expected to produce more fallout, it was decided to conduct the tests in a more remote location.
2 islands in the Pacific Ocean were selected. Chrismas Island, which would be the base for the test force, and Malden Island, located some 360 miles south would be the test site. However, after the first round of tests, to save time and money, the second round of tests would be carried out, offshore of Christmas Island.
A total of 9 tests were conducted, all air burst to reduce the risk of fallout. 7 of the tests, the device was deployed from Vickers Valiants bombers and 2 were tethered from barrage ballons.
Construction of the base on Chrismas Island commenced during 1956. A new 7,000 foot runway was built, and additional 25 miles of new roads constructed, together with buildings and housing (mostly tents) put together for the 1200 personnel. This was sited on the northern end of the Island
A Tri-Service task force: “Task Foce 308” was formed, and the RAF element, No.160 wing was formed at RAF Hornchurch in the spring of 1957.
No.206 and No.240 Squadrons RAF provided Avro Shacketon Mk2s for Maritime Search and Reconnaisance.
No.49 Squadron RAF provided Vickers Valiant bombers for the drop tests.
No.76 Squadron RAF provided 6 EE Canberrra B.6 for radition sampling.
No.100 Squadron provided 4 EE Canberra PR.7 for long range weather reconnaisance.
No.58 Squadron provided to EE Canberra PR.7 to fly radioactive samples back to the UK.
15 May 1957, codename ‘Short Granite’, Valiant XD818 dropped a 1 megaton device which exploded 8,000 feet above Malden Island. Only a 300 kiloton yield was achived from the device.
31 May 1957 codename ‘Orange Herald’, this was actually a fission bomb, which detonated with a 720 kiloton yield.
19 June 1957, codename ‘Purple Granite’, another poor yield of 200 kilotons.
Grapple 1 tests were a disapointment to the British government as the yields were much lower than expected. However, much had been learned and changes made for the next round of testing.
It was decided to do another set of testing as part of Grapple X, Grapple Y and Grapple Z.
8 November 1957, Valiant XD824 dropped a device offshore of Christmas Island, the yield was much bigger than expected at 1.8 megatons. The blast caused some structural damage to the base on the north of the island, 24 miles away.
28 Apirl 1958, Valiant XD825 dropped the UKs first true Hydrogen bomb, the yield was 2 megatons.
Grapple Z was a series of 4 tests of lower yields, 2 tests were air dropped and 2 were balloon deployed.
22 August 1958, codename ‘Pendant’, the device was suspended under 4 barrage balloons, a yield of 24 kilotons was recorded.
2 September 1958, codename ‘Flagpole’, dropped by Valiant XD822, a yield of 1.2 megatons was achived.
11 September 1958, codename ‘Halliard 1’, dropped by Valiant XD827, a yield of 800 kilotons was achived.
23 September 1958, codename ‘Burgee’, the device was suspended under barrage balloons and yielded 25 kilotons. This was the UKs last ever atmospheric nuclear test.
After the tests
Britain never developed any H-bombs from the Grapple designs. However the later Green Grass atomic fission bomb was developed from the ‘Orange Herald’ fission device.
Another benefit from the testing, is that the USA realised that it was time to start sharing nuclear weapon technology with the UK. This benefited both sides, as the USA soon realised that the UK was ahead in some areas such as electronics and circuitry for thermonuclear weapons.
The Aircraft (images not to scale)
Royal Air Force Vickers Valiant, No 49 Squadron.