Operation Grapple X

Operation Grapple X - 1957

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The disappointing results of Grapple necessitated further trials. While Grapple was a political success, scientifically it had not fulfilled the original goal of producing a one-ton/one-megaton weapon. The Soviet Sputnik 1 launch in October 1957 presented an opportunity for the British to renew nuclear cooperation with the United States. The Sputnik 1 launch indicated the Soviet Union could hit a target anywhere in the world using the crude ICBM. A megaton test by the British would surely help the chances of establishing nuclear defense cooperation between the United States and Great Britain.

Operation Grapple X was planned for the fall of 1957. The purpose of this operation was to achieve a true, thermonuclear yield. The first Grapple operation was merely a test of a two-stage weapon, Grapple X would be a test of an efficient version of this principle. With an imminent nuclear testing moratorium, preparations proceeded at a hectic pace. While the first Grapple operation was planned over the course of several years, the planners now had only months.

The HMS Narvik and HMS Warrior would not be available for Grapple X so as a result it was planned to conduct the trials off Christmas Island instead of Malden Island. A major task confronted the Royal Engineers in improving the existing Christmas Island infrastructure as well as relocating the Malden Island instrumentation.

While preparation of the test site was underway, development of the test devices proceeded. The new IBM 704 computer, delivered to Aldermaston in the summer of 1957, was used extensively for calculations by the design team. A modified Red Beard fission bomb would be used as the primary for the device. It had an improved high explosive assembly, a beryllium tamper, and a cartridge loading tube as a safety device allowing last-minute loading. For the Dick secondary, the amount of Uranium-235 was increased as well as the thickness of the lithium-deuteride layers.

Three major goals were presented to the development team. One was to generate a megaton yield using minimal amounts of fissile material, in the event of an international bad on fissile material production. Secondly, yields of 5-10 megatons would need to be achieved in subsequent nuclear devices. Thirdly, the thermonuclear warheads would need to be immune to radiation-intensive enemy nuclear attacks. All of these aspects were considered in the development of the Grapple X devices.

Image source: BCWSW
The Round A bomb

A target date of November 5, 1957 was set for the first shot of the series. All construction and installation work had to be completed by October 23. 26 blast proof steel shelters were built on Christmas Island since the move of testing from Malden Island. Some of these shelters were fitted with equipment from the HMS Narvik. 15 miles from the intended ground zero on the east end of the island a tented camp for 100 men, including 28 Aldermaston staff, was erected. Due to complaints about the poor living conditions on Christmas Island during the first Grapple operation, efforts were made to increase the standard of food. Air Commodore 'Ginger' Weir ordered the number of cooks and butchers to be doubled.

By early August, an initial sequence of test rounds was made for the Grapple X trials:

Round A: Three-layer secondary device
Round B: Five-layer secondary (only fired if fast-neutron yield in Round A was satisfactory)
Round C: Three-layer secondary with an inert layer replacing the lithium-deuteride (only fired if fast-neutron yield in Round A was unsatisfactory)
Round D?: Test of a single primary stage to check yield (only fired if Round C showed low Uranium-235 yield)

Image source: BCWSW
American observers arrive at Christmas Island for Grapple X

The casing for Round A was the same size used for Short Granite and the primary stage would be 50% more powerful. The production of the weapon components met many delays. Lithium-6 stocks were insufficient for the current tentative designs being developed and enough could not be manufactured to meet the shot deadlines. Also shortages of personnel and delays in the transfer of physics requirements further hampered production. The possibility of have three devices ready for the Grapple X trial was small. Delays in the computer calculations of the multi-layered systems resulted in the eliminating of one round from the test. Grapple X was now down to three shots.

By September 16 the Round C device design was settled an estimated date of delivery was made. Round B was also canceled from the Grapple X trials due to time need for calculations for the Round A Dick component. The Round A components would eventually meet the November 5 deadline. A danger zone was approved for Grapple X and went into effect on November 1. The danger zone was created on the assumption that no test would exceed 2 megatons.

Despite the delays in the development of the test devices, the pieces were quickly falling into place and the Grapple X trials were only weeks away.

The Test

Code Name: Grapple X - Round A
Time and Date: 17:47 November 8, 1957 (GMT)
Location: Christmas Island
Height: 7200 Feet
Type: Air Drop
Predicted Yield: 1000 kilotons (<2000 kilotons)
Actual Yield: 1800 kilotons
Image source: AWRE
In the end of October the Personnel Safety Plan was issued. It was essentially the same as the Grapple safety plane though modifications were made since the location of the test was moved from Malden Island to Christmas Island. The native population of Christmas Island would embark on the HMS Messina during the tests. Personnel remaining on the island would have to cover as much of their bodies as possible. Ed Fuller, the chief health physicist, would lead the first re-entry into the forward area after the blast, which was strictly controlled.
On October 18 the bomb components began to arrive at Christmas Island. These included the components for the actual nuclear devices as well as the rehearsal bombs. At this point, the firing program consisted of the following shots:
Round A: three-layer secondary
Round C: one inert layered seconday

Image source: BCWSW
The Round A bomb was loaded onto the Valiant behind canvas screen

Nearly all of the Round A and Round C components arrived at Christmas Island on October 24,27, and 29. These were then taken to the weapon assembly area for inspection and radiography. The only component that had not arrived was the primary for Round C.
However, faults had been discovered in the Round A primary which may have developed during its shipment to Christmas Island. The primary for Round C would be used for the Round A device and a replacement primary would be sent out the Christmas Island for Round C.
Another problem arose with the fissile core for the Round C primary that was delivered on October 29 and was now needed urgently for Round A. The core became stuck in it's container and would not come loose. To resolve this problem, the container with the fissile core was placed in hot water for 15 minutes. The ball then was collected without any trouble.
Image source: BCWSW
Waiting for the explosion

The following day the core was taken to the explosives assembly building and fitting into the Tom primary. Work on the primary went on round the clock and finished on October 31. The core was then brought into the weapon assembly building and installed into the casing. The next day a mobile crane brought the Dick secondary from its humidity-controlled building into the weapons assembly building where the two stages were bolted together. The warhead was then installed into the Blue Danube bomb casing.
The bomb was ready for testing by November 5, the intended deadline, but rains pushed back the firing date by three days. Despite the rains, the operational rehearsal was conducted on November 5. On Thursday, November 7, Round A was loaded on the Valiant drop plane which was piloted by Squadron Leader Barney Millett. A guarded barrier was set up around the perimeter to prevent unauthorized access.
Image source: BCWSW

The next day was D-day. A small crisis arose when a Shackleton on a routine sea search found a Liberian ship sailing in the danger zone. The ship, Effie, was an old World War II Victory ship that had probably set sail before being notified of the restricted area. Contact could not be made with the ship and it was kept under constant observation by the Shackletons. Meanwhile, the Task Force frigate HMS Cossak steamed to intercept her and hoped to reach her in four hours. Eventually, contact was made with the Effie at 6:15 AM by one of the Shackletons by dropping leaflets. Effie turned south and steamed away at 12 knots, she would clear the danger zone in time.
At 8:45 AM local time, the Grapple X device was dropped off Christmas Island. The release of the bomb activated the telemetry recording instruments on the island which were focused on the intended zero point of the explosion. The Valiant then proceeded in its escape the maneuver as the bomb fell for 53 seconds. The bomb exploded with a force of 1.8 megatons and created a fireball over a mile in diameter.
The bomb missed its intended burst point by 320 yards to the left and 32 yards beyond. The bomb caused some damage to the infrastructure on the island and repairs were needed. Helicopter windows were blown out, aircraft fuel storage tanks were ruptured 26 miles from ground zero, and a large area of land was scorched by the explosion.

Grapple X Video
The following footage of the Grapple X explosion was filmed from the ground from two different angles. The first sequence is a wide angle view of the explosion filmed from Christmas Island. The brilliant flash of the explosion fills the entire frame, followed by a good view of the rising fireball and formation on several condensation rings. The second sequence was filmed much closer to ground zero and shows the rapidly rising and cooling fireball. Several condensation structures are visible in this sequence, including the formation of an ice cap and a bell forming under the center of the toroidal fireball. Click on the thumbnail image to the left to watch the video.
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Footage source: Britain's Cold War Superweapons
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Grapple X Aftermath
Image source: BCWSW
Grapple X damage

The Round A shot was highly successful and resulted in the cancellation of the Round C shot. Early British estimates placed the yield of the explosion at 1.4 to 1.6 megatons. American estimates put the yield at 3 megatons based on comparisons of 3 to 5 megatons to certain Soviet tests. Photographic measurements of the fireball placed the yield closer to 1.8 megatons. Radiochemical samples obtained by the 'sniffer' aircraft proved to be unreliable.
Grapple X secured Britain's place among the thermonuclear club. Date obtained from the successful explosion made invaluable contributions to research on the physics of thermonuclear weapons. Further trials would now be needed to advance this new understanding.

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