Grapple series (3 tests) test, it was in fact a failure. The first trial series consisted of three tests, named
Grapple 1,
Grapple 2 and
Grapple 3. All bombs were dropped and detonated over Malden Island, and exploded
high in the atmosphere, rather than being detonated
on the ground, in order to reduce the production of
nuclear fallout. British scientists were aware that the Americans had been able to reduce fallout by obtaining most of the bomb yield from fusion instead of fission, but they did not yet know how to do this. Amid growing public concern about the dangers of fallout, particularly from
strontium-90 entering the food chain, a committee chaired by Sir
Harold Himsworth was asked to look into the matter. Another, in the United States chaired by
Detlev Bronk, also investigated. They reported simultaneously on 12 June 1956. While differing on many points, they agreed that levels of strontium-90 were not yet sufficiently high to be of concern. At an altitude of , the fireball would not touch the ground, thereby minimising fallout. The bombs would be detonated with a clockwork timer rather than a barometric switch. This meant that they had to be dropped from in order to detonate at the correct altitude. Grapple was Britain's second airdrop of a nuclear bomb after the
Operation Buffalo test at
Maralinga on 11 October 1956, and the first of a thermonuclear weapon. The United States had not attempted this until the
Operation Redwing Cherokee test on 21 May 1956, and the bomb had landed from the target. Aldermaston wanted the bomb within of the target, and Oulton felt that a good bomber crew could achieve that. A exclusion zone was established, covering the area between 3.5° North and 7.5° South and 154° and 163° West, which was patrolled by Shackletons. No. 49 Squadron had eight Valiants, but only four deployed: XD818, piloted by
Wing Commander Kenneth Hubbard, the squadron commander; XD822, piloted by
Squadron Leader L. D. (Dave) Roberts; XD823, piloted by Squadron Leader Arthur Steele; and XD824, piloted by Squadron Leader Barney Millett. The other four Valiants remained at
RAF Wittering, where they were used as courier aircraft for bomb components. The last components for Short Granite were delivered by Valiant courier on 10 May 1957—three days late owing to severe head winds between San Francisco and Honolulu. A full-scale rehearsal was held on 11 May, and on 14 May it was decided to conduct the Grapple 1 test the following day. The eight official observers—two each from Australia, Canada, New Zealand and the United States—were flown from Honolulu to Christmas Island in an RAF Hastings, then to Malden Island in a Dakota, from whence a DUKW took them out to HMS
Alert, the spectator ship. All but a small party were evacuated from Malden by HMS
Warrior,
Narvik and
Messina by 19:00 on 14 May. The rest were picked up by a helicopter from
Warrior at 07:45 on 15 May. Oulton and Cook arrived on Malden by Dakota at 08:25, where they were met by a helicopter and taken to
Narvik. The Grapple 1 mission was flown by Hubbard in XD818, with Millett and XD824 as the "grandstand" observation aircraft. The two bombers took off from Christmas Island at 09:00. The bomb was dropped from off the shore of Malden Island at 10:38 local time on 15 May 1957. Hubbard put the bomb from the target. The bomb's yield was estimated at , far below its designed capability. Penney cancelled the Green Granite test and substituted a new weapon codenamed Purple Granite. This was identical to Short Granite, but with some minor modification to its Dick: additional uranium-235 was added, and the outer layer was replaced with aluminium. Despite its failure, the Grapple 1 test was hailed as a successful thermonuclear explosion, and the government did not confirm or deny reports that the UK had become a third thermonuclear power. When documents on the series began to be declassified in the 1990s, they created a spirited debate among nuclear historians. Norman Dombey and Eric Grove denounced the Grapple tests in the
London Review of Books in 1992 as a hoax intended to deceive the Americans into resuming nuclear cooperation, but others, like the British nuclear weapons historian John Bayliss, pointed out that false reports would not have fooled the American observers, who helped to analyse samples from the radioactive cloud. , as reported by Universal International Newsreel The next test was Grapple 2, of Orange Herald (small). For this test, two Fijian official observers were added. A detachment of 39 Fijian
Royal Navy Volunteer Reserve ratings who had been on board RNZN
Pukaki and
Roititi was transferred to HMS
Warrior. This time there were also media representatives present on HMS
Alert, including
Chapman Pincher and
William Connor. Orange Herald bomb components arrived in three separate loads on 13 May. Assembling them took two weeks. The bomb was dropped by XD822, piloted by Roberts, while XD823, piloted by Steele, acted as the grandstand aircraft. This bomb was dropped at 10:44 local time on 31 May. After the bomb was released, Roberts made the standard 60° banked turn to get away, but his
accelerometer failed, and the aircraft went into a high speed
stall. This was potentially disastrous, but through skilful flying Roberts was able to recover from the stall and use the mechanical accelerometer to complete the manoeuvre. The yield was the largest ever achieved by a single stage device. This made it technically a megaton-range weapon; but it was close to Corner's estimate for an unboosted yield, and there were doubts that the lithium-6 deuteride had contributed at all. This was attributed to
Rayleigh–Taylor instability, which limited the compression of the light elements in the core. The bomb was hailed as a hydrogen bomb, and the fact that it was actually a large fission bomb was kept secret by the British government until the end of the
Cold War. The third and final test of the series was Grapple 3, the test of Purple Granite. This was dropped on 19 June by a Valiant XD823 piloted by Steele, with Millett and XD824 as the grandstand aircraft. The yield was a very disappointing , even less than Short Granite. The changes had not worked. "We haven't got it right", Cook told Oulton. "We shall have to do it all again, providing we can do so before the ban comes into force; so that means as soon as possible."
Grapple X (1 test) The next test series consisted of a single trial known as Grapple X. To save time and money, and as HMS
Warrior,
Alert, and
Narvik were unavailable, it was decided to drop the bomb off the southern tip of Christmas Island rather than off Malden Island. This was just from the airfield where 3,000 men were based. It required another major construction effort to improve the facilities, and some of those on Malden Island now had to be duplicated on Christmas Island. Works included 26 blast-proof shelters, a control room, and tented accommodation. To provide some means of chasing away intruders, the
destroyer was allotted. HMNZS
Rotoiti and
Pukaki reprised their role as weather ships. A cargo ship, the SS
Somersby was chartered to bring tentage and stores to Christmas Island. Monitoring equipment was set up on Malden Island and Fanning Island, and the observation posts on Penrhyn Island and
Jarvis Island were re-established. Oulton noticed that: While some ships and units such as No. 49 Squadron returned to the UK, most personnel had to remain on Christmas Island. The
Minister of Supply gave assurances that no personnel would have to remain on the island for more than a year unless absolutely necessary, in which case home leave would be given. To maintain morale, units were given periodic briefings on the importance of their work. Junior officers took a keen interest in the welfare of the men and their families at home, since they were not permitted to bring them to the island. An efficient mail system was maintained to allow them to keep in contact. The quality of Army rations was better than at any other British base. The men were given one day a week off work, and sports such as
football, cricket, tennis, volleyball, sailing, fishing and water skiing were organised. Leave was provided that could be taken in Fiji, Hawaii or the Gilbert Islands. To relieve the monotony, some Army personnel ashore exchanged places with some Navy personnel afloat. A Christmas Island Broadcasting Service was established with nightly radio programmes. The scientists at Aldermaston had not yet mastered the design of thermonuclear weapons. Knowing that much of the yield of American and Soviet bombs came from fission in the
uranium-238 tamper, they had focused on what they called the "lithium-uranium cycle", whereby neutrons from the fission of uranium would trigger fusion, which would produce more neutrons to induce fission in the tamper. However, this is not the most important reaction. Corner and his theoretical physicists at Aldermaston argued that Green Granite could be made to work by increasing compression and reducing Rayleigh–Taylor instability. The first step would be achieved with an improved Tom. The Red Beard Tom was given an improved high explosive supercharge, a composite uranium-235 and plutonium core, and a
beryllium tamper, thereby increasing its yield to . The Dick was greatly simplified; instead of the fourteen layers in Short Granite, it would have just three. This was called Round A; a five-layer version was also mooted, which was called Round B. A diagnostic round, Round C, was also produced. It had the same three layers as Round A, but an inert layer instead of lithium deuteride. Grapple X would test Round A. Components of Rounds A and C were delivered to Christmas Island on 24, 27 and 29 October. On inspection, a fault was found in the Round A Tom, and the fissile core was replaced with the one from Round C. This time there was no media presence, and only two foreign observers,
Rear Admiral G. S. Patrick, the Director of the Atomic Energy Division in the Office of the
Chief of Naval Operations from the US Navy, and
Brigadier General John. W. White, the Deputy Chief of the
Armed Forces Special Weapons Project, from the USAF. As the final preparations were being made for the test on 8 November, Oulton was advised at 01:00 that a Shackleton had sighted the SS
Effie, an old
Victory ship now flying the Liberian flag, in the exclusion zone. Eager to minimise publicity before this test, the British government had delayed sending out the
Notice to Mariners, which had only been issued three weeks before. This failed to take into account the size of the Pacific Ocean;
Effie had left its last port of call before it had been issued. The Shackleton kept
Effie under observation while trying to contact her, and
Cossack was sent to intercept. By 06:00, all was in readiness for the test, but there was no news of
Effie. Finally, at 06:15, word was received from the Shackleton that the crew had woken up and
Effie had turned about and was now headed due south, out of the exclusion zone at . A report from the Shackleton at 07:25 indicated that
Effie was now sailing in company with
Cossack. By this time the Valiants had started their engines; they took off at 07:35, and were on the way when
Cossack reported that
Effie had cleared the area. The bomb was dropped from Valiant XD824, piloted by Millett, at 08:47 on 8 November 1957; Flight Lieutenant R. Bates flew the grandstand Valiant XD825. This time the yield of exceeded expectations; the predicted yield had only been , but it was still below the safety limit. This was the real hydrogen bomb Britain wanted, but it used a relatively large quantity of expensive
highly enriched uranium. Due to the higher-than-expected yield of the explosion, there was some damage to buildings, the fuel storage tanks, and helicopters on the island.
Grapple Y (1 test) The physicists at Aldermaston had plenty of ideas about how to follow up Grapple X, and the possibilities were discussed in September 1957. One was to adjust the width of the shells in the Dick to find an optimal configuration. If they were too thick, they would slow the neutrons generated by the fusion reaction; if they were too thin, they would give rise to Rayleigh–Taylor instability. Another was to do away with the shells entirely and use a mixture of uranium-235, uranium-238 and deuterium. Ken Allen had an idea, which
Samuel Curran supported, of a three-layer Dick that used a greater amount of lithium deuteride that was less enriched in lithium-6 (and therefore had more lithium-7) while reducing the amount of uranium-235 in the centre of the core. This proposal was adopted in October, and it became known as "Dickens" because it used Ken's Dick. The device would otherwise be similar to Round A, but with a larger radiation case. The safety limit was again set to . Keith Roberts calculated that the yield could reach , and suggested that this could be reduced by modifying the tamper, but Cook opposed this, fearing that it might cause the test to fail. The possibility of a moratorium on testing caused the plans for the test, codenamed Grapple Y, to be restricted to the Prime Minister,
Harold Macmillan, who gave informal approval, and a handful of officials. The
New Zealand National Party lost the 1957 election, and
Walter Nash became prime minister. His
New Zealand Labour Party had endorsed a call by the
British Labour Party for a moratorium on nuclear testing, but he felt obligated to honour commitments made by his predecessors to support the British nuclear testing programme. However, HMNZS
Rotoiti was unavailable, as it was joining the
Far East Strategic Reserve; its place would be taken by the destroyer . Air Vice Marshal
John Grandy succeeded Oulton as Task Force commander, and Air Commodore Jack Roulston became the Air Task Force Commander. The bomb was dropped off Christmas Island at 10:05 local time on 28 April 1958 by a Valiant piloted by Squadron Leader Bob Bates. It had an explosive yield of about , and remains the largest British nuclear weapon ever tested. The design of Grapple Y was notably successful because much of its yield came from its thermonuclear reaction instead of fission of a heavy uranium-238 tamper, making it a true hydrogen bomb, and because its yield had been closely predicted—indicating that its designers understood what they were doing.
Grapple Z series (4 tests) On 22 August 1958, US President
Dwight D. Eisenhower announced a
one-year moratorium on nuclear testing, effective 31 October 1958, if the Soviet Union and the United Kingdom also agreed to suspend testing. Britain had already indicated that it would do so, and the Soviet Union agreed on 30 August. This did not mean an immediate end to testing; on the contrary, all three rushed to perform as much testing as possible before the deadline. The British scientists needed to gather as much data as possible to allow them to design production nuclear weapons. As the prospect of increased American cooperation grew after October 1957, they knew that the quality and quantity of what the Americans would share would depend on what they had to offer. A new British test series, known as Grapple Z, commenced on 22 August. It explored new technologies such as the use of external neutron initiators, which had first been tried out with Orange Herald. Core boosting using
tritium gas and external boosting with layers of
lithium deuteride permitted a smaller, lighter Tom for two-stage devices. It would be the biggest and most complex British test series. Of particular concern was radiation damage. Keith Roberts and
Bryan Taylor at Aldermaston had discovered that the flash of radiation from the detonation of an atomic bomb could affect a nearby bomb. This opened up the possibility of a missile warhead being disabled by another launched for this purpose. Plutonium cores were especially vulnerable, as they were already prone to
predetonation. This had the potential to render Britain's nuclear deterrent ineffective. This discovery was given the highest level of secrecy, and Aldermaston would spend much of the next few years working on the problem. To build a primary immune to this effect would require techniques that Aldermaston had not yet mastered. The number of tests in the series was assumed to be four for planning purposes, but as late as May the Prime Minister had only approved two tests, tentatively scheduled for 15 August and 1 September 1958. Four Valiants, XD818, XD822, XD824 and XD827, deployed to Christmas Island, the last of which arrived on 31 July. The first test was of Pendant, a fission bomb boosted with solid lithium hydride intended as a primary for a thermonuclear bomb. Rather than being dropped from a bomber, this bomb was suspended from a string of four vertically stacked
barrage balloons. This was chosen over an air drop because the bomb assembly could not be fitted into a droppable casing, but it introduced a host of problems. A balloon test had been tried only once before by the British, during
Operation Antler at Maralinga in October 1957. William Saxby from Aldermaston was placed in charge of the balloon crews, who commenced training at
RAF Cardington in
Bedfordshire in January 1958. Inflating the balloons required 1,200 cylinders of
hydrogen gas, and there were no reserves. If another balloon test was required, then the empty cylinders would have to be returned to the United Kingdom for refilling, and then shipped out again. An important consideration was how they could be shot down if they broke loose of their moorings with a live nuclear bomb. The cargo ship SS
Tidecrest arrived at Christmas Island on 20 July, but the firing harness was lost at
San Francisco International Airport on 1 August, and a replacement had to be flown out. The Pendant fissile core arrived by air on 12 August, and the weapon was assembled with its external neutron initiator unit. On 22 August 1958 it was hoisted in the air over the south east corner of Christmas Island, and it detonated at 09:00. The yield was assessed at . The next test was of Flagpole, a scaled down version of the Grapple Y device with a small, unboosted primary known as Indigo Herald. It was air dropped by Valiant XD822, flown by Squadron Leader Bill Bailey, with XD818 flown by Flight Lieutenant Tiff O'Connor as the grandstand aircraft, on 2 September 1958. This was the first live drop of a British nuclear weapon using blind radar technique. This meant that the bomb would be dropped using radar rather than visually with the optical bombsight, a technique normally reserved for when a target is obscured by cloud or smoke. Bailey managed to place the bomb from the target. It detonated at about offshore from South East Point on Christmas Island at 08:24 with a yield of about . The third test was of Halliard, an unusual three-stage design with two nuclear-fission components followed by a thermonuclear stage that was supposedly immune to exposure from another bomb despite its not using boosting. The Americans had indicated an interest in it. Macmillan noted in his diary: The success of blind radar bombing in Flagpole led to Grandy deciding to use the technique again. Hubbard was less sure. The accuracy achieved in Flagpole was exceptional; in 52 practice drops with blind radar, the average error had been as opposed to with visual bombing. Thus it was only slightly more accurate, but the aircrew would be dropping a live hydrogen bomb—generally considered a dangerous thing to do—with no means of verifying that their instruments were correct.
Air Chief Marshal Sir
Harry Broadhurst, the head of
Bomber Command, wished O'Connor luck; his XD827 would make the drop, with Squadron Leader Tony Caillard in XD827, the grandstand aircraft. The aircraft took off at 07:15 on 11 September 1958. Once in the air, a fault developed in the ground radar transmitter. Grandy then authorised a visual drop. It was later confirmed that it was from the target. It was detonated at about offshore from South East Point on Christmas Island at 08:49 with a yield of about , very close to the predicted yield of . The final test in the Grapple Z series was of Burgee, at 09:00 on 23 September 1958. This was another balloon-borne test detonated over the south east corner of Christmas Island. Burgee was an atomic bomb boosted with gaseous
tritium created by a generator codenamed Daffodil. It had a yield of about . The Aldermaston weapon makers had now demonstrated all of the technologies that were needed to produce a megaton hydrogen bomb that weighed no more than and was immune to premature detonation caused by nearby nuclear explosions. The international moratorium commenced on 31 October 1958, and Britain never resumed atmospheric testing.
Summary } Caused damage to buildings on Christmas island, some even caught fire. ==Aftermath==