Home : Britain's Nuclear Weapons Program
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Operation Grapple was conducted at Christmas and Malden Islands in the spring of 1957. The purpose of Operation Grapple was to test four prototype nuclear weapons, each on the order of one megaton. Even before the final designs of the tests devices was settled, detailed preparations for Grapple began in the autumn of 1955. Since it was originally planned to test a wide variety of nuclear devices in the pacific, Grapple was arranged to accommodate that contingency. The development of the test devices and preparation of the test site at Christmas Island went on simultaneously. Four weapon designs were added to the Grapple itinerary:
The radiation implosion stage implemented on the Green Granite device was discussed at Aldermaston at least as far back as January 1955. It was hoped that all weapons would be ready for firing by July 1, 1957.
Due to Britain's limited experience with nuclear weapons, the success of the designs was far from certain. It was anticipated, by Penney as well as others, that these experimental thermonuclear devices may only produce yields of 200-300 kilotons. This would indicate to the world that Britain had not yet achieved a position to produce and use the hydrogen bomb. An operation order based on success was implemented for the nuclear shot timetable. If Green Bamboo, the spherical thermonuclear device, failed to achieve a megaton yield, then a 'special assembly' (Orange Herald (Large))device would be fired. If Green Bamboo was successful, then Orange Herald (Small), an experimental ballistic missile warhead, would be fire and not the 'special assembly'. Green Bamboo and Orange Herald used large amount of fissile material. The experimental double bomb, Green Granite, was hoped to reach a megaton yield using much less fissile material then used in the Green Bamboo and Orange Herald devices. Safety was a major priority for the Grapple planners. Experience gained in the Australian testing operations would be a major asset for planning safety parameters for the firing of the much larger (it was hoped) thermonuclear devices. Grapple did present a variety of new challenges for the planners. Among them were the variables involved in conducting airdrops of nuclear weapons since all prior nuclear tested conducted by Britain had been tower or surface shots. Particular attention was paid by the Atomic Weapons Trails Executive on the question of bomber safety on take-off. Of primary concern was the event of the bomber's crash on take-off with a nuclear payload and the safety of all personnel on the island. Another concern was if the device failed to detonate at the predetermined height and a surface burst resulted. Arrays of instruments and cameras were installed at the site which would be aimed directly at the air burst. These instruments would collect data on, among other things, the performance of weapon electronics, measurement of blast pressure, measurements of thermal, gamma and blast effects on the Valiant bomber and high speed photography of the expansion of the initial burst of energy. Radiochemical analysis would be conducted on samples collected by special 'sniffer' aircraft flying through the radioactive mushroom cloud following an explosion. The program had been revised by January 1956 and it was expected that the test devices would be ready by December 31. Six inert weapons would be needed to test the weapon's telemetry systems and for operational rehearsals. These weapons would contain high explosives instead of nuclear assemblies. 22 bomb casings in total were planned for the trial by the RAF and Aldermaston. Each weapon would have fixed time, clockwork fuses instead of barometric ones. To conduct an air burst at 8,000 feet would require a drop from an altitude of 45,000 feet. In the event of a clockwork fuse malfunction, safety devices would ensure that a nuclear detonation would not take place and as an added precaution an Impact Sterilising Swith (ISS) was installed on each device to disable the firing circuits on impact with the sea.
Other safety issues for Grapple was handling and cleaning of the 'sniffer' cloud sampling aircraft and the handling of their radioactive samples. Detailed procedures for Operation Grapple included those for Operation Falcon, the direct non-stop flight of Canberra aircraft to Blackbushe airport near Aldermaston to deliver the fresh cloud samples. Accurate meteorological information was essential in conducting any nuclear test. For this task, Ernest Hicks, an expert of fall-out prediction from Aldermaston's theoretical physics division, would be present at Christmas Island to work with the meteorological staff. The declared danger zone around the test site for the nuclear shots was constantly revised. Initally a rectangle 150 miles by 20 miles downwind of the burst along with a circle 40 miles in diameter around ground zero was planned. This was later changed on June 19, 1956 to cover an area about 540 to 660 nautical miles. Two months later this area was once again enlarged based on new meteorological information. The patrols of the danger area would be conducted by Shackleton aircraft. Detailed contingency plans were also made during this time on the evacuation of Christmas Island in the event of an accident involving the nuclear device. The HMS Narvik was assigned to be the technical control ship for the operation. However, the Narvik was involved with the nuclear tests in Australia and it was unknown at the time if she could make the target date, now April 1, 1957, for the Grapple trials. By the end of April, the Green Granite design was approved and frozen for the Grapple trial. After several modifications, the Green Bamboo design was also approved and frozen. Green Bamboo included lithium tritide powder and 700 pounds worth of steel balls to be inserted into the fissile core for safety reasons. These balls would be removed prior to arming. Operation Mosaic was underway at the time in Australia. Two experimental devices were fired, G1 and G2. G1, detonated on May 16, 1956, had a yield of 15 kilotons. This yield was much lower then predicted and resulted in the test of the G2 device with a uranium tamper. Fired on June 19, 1956, Mosaic had a yield of 98 kilotons. With the testing of the G2 device with a uranium tamper, the G2 test was removed from Operation Grapple. Two versions of the boosted fission bomb were under development at Aldermaston; Orange Herald (Large) and Orange Herald (Small). The difference in design was the high explosive assemblies, not the boosted fissile cores. These designs were frozen in July. With the devices modifications and final design approvals, the firing order for Grapple now stood as: If Short Granite resulted in a successful yield, then Green Bamboo would not be fired. Orange Herald would still be fired since both Granite devices were too large for a ballistic missile warhead.
Finals preparations for both the test devices and test sites reached a hectic pace in the months and weeks leading to the first shot. Major concerns for the Grapple planners included radiation safety standards, danger area finalization, contamination of fish in the surrounding ocean, actions to be taken in the event of an accident, diagnostic measurement for each shot, and over-flying permissions to transport the test devices to Christmas Island. By December 1956, there were nearly 4,000 men stationed on Christmas Island for Operation Grapple. By January 1957 almost all of the domestic, technical, and operational facilities on the atoll were complete. These final months of preparation included scientific and operational tasks, such as the testing of equipment, setting up instrumention, continuing the special training of the Valiant bomber crew and the establishment of a meteorological station on Christmas Island. The HMS Narvik, which had received an extensive refit at Portsmouth following Hurricane and Mosaic, sailed for Christmas Island. She would act as the command post and scientific control center for the drops off Malden Island. During her voyage across the Atlantic she developed cracks in her deck plating which were repaired in Jamaica. She then passed through the Panama Channel, with only inches to spare on either side of the ship, since sailing around Cape Horn would take too long. During April test drops of dummy bombs were conducted. This provided the opportunity for the scientists to calibrate and test their telemetry equipment as well as provide needed practice for the Valiant bomber crews to perfect their bombing accuracy. Accuracy was essential as the instruments were focused on a special part of the sky where the devices would explode. By May, Grapple was ready for the first test. |
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The results of Operation Grapple were mixed. The yields of the experimental thermonuclear devices were disappointing as a megaton yield was not reached. The American observers were well aware of the disappointment felt by the British. However, much valuable information was learned from the Grapple shots. The Short Granite device worked well and produced a substantial thermonuclear yield. The radiation implosion design was confirmed and valuable data was acquired which would lead to a true hydrogen bomb. The airdrops were conducted with great skill and precision. The entire operation was conducted with admirable safety. Though disappointing, Operation Grapple was by no means a failure. The tests were hailed by the British government as proof that Britain had indeed mastered the hydrogen bomb. This was inaccurate and the government prevented the publishing of the true nature of the tests by press. While not megaton range weapons, Short Granite and Purple Granite were technically hydrogen bombs since fusion reactions contributed to a substantial amount of their respective yields. It had been hoped that further hydrogen bomb trials would not be needed after Operation Grapple, however, it had not been a realistic hope. The disappointing results of the Granite shots confirmed that further tests would be needed. Operation Antler, conducted at Maralinga later that year, sought to test a primary device which would be incorporated into the new thermonuclear weapon. Shortly after the tests, preparations were already underway for the next Grapple series, Grapple X.
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