Abstract
Weeks before Grapple X in November 1957, and months before Grapple Y in April 1958, the next trial — Grapple Z — was already being considered. All three trials were part of a programme of development which had to be flexible because plans for later shots, and the order in which they were fired, depended largely on the results of the earlier ones. They also depended on larger contingencies — the encouraging prospects of renewed Anglo-American nuclear co-operation, and the pressures of public opinion and worldwide concern about fall-out which would make a test ban or moratorium inevitable sooner rather than later.
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Notes and References
The two Windscale production reactors had both been closed after the October 1957 fire in one of them, and the new reactors at Calder Hall were only just coming into production.
L. Arnold, A Very Special Relationship, pp. 185–6.
Scientists not privy to super-secret information about ‘RI’ concluded that ‘DP’ stood for ‘dirty plutonium’ and that these bombs contained more highly irradiated plutonium than normal.
The difference between the two was in the amount of U-235 in the secondary.
The design is usually referred to as Pendant but the test is most often called Pennant. Pennant seems more appropriate than Pendant, in keeping with the other names used — Flagpole, Burgee, Halliard and Ensign.
The difference between the large and small versions of Burgee was not in the boosting but in the implosion and detonation systems.
Grapple Z sequence I If (a) round 1 (Pendant) or round 3 (Burgee) yielded more than 14 kT and (b) round 2 (Flagpole) was successful then no Halliard round would be fired. II If the better of the two yields from rounds 1 and 3 (Pendant and Burgee) was intermediate, then Halliard 2 (double bomb) would be fired as round 4. III If the better of two yields from rounds 1 and 3 (Pendant and Burgee) was poor then Halliard 1 (triple bomb with thick case) would be fired as round 4. IV If rounds 1, 2 and 3 (Pendant, Flagpole and Burgee) were all successful then Halliard 3 (triple bomb with thin case) should be made ready to fire as round 4. In the event, conditions 1(a) and (b) were met and so no Halliard round was necessary. But Halliard 1 was fired at American request.
Aldermaston collaborated on this innovatory design (see pp. 178, 185, 207) with SERL, the electronics research laboratory at Baldock, Hertfordshire.
This was not a dose which would lead to any perceptible symptoms. It was however equivalent to the ‘higher integrated dose’ permissible in exceptional circumstances with advance approval (see Appendix 4).
Not all the lithium hydride blocks apparently. Some were taken to a remote part of the south-west coast of Christmas Island, for a variety of ad hoc experiments. They were unwrapped and exposed to air, sprayed with water, and then completely immersed. Finally came an attempt to burn them on a bonfire, aided by two gallons of petrol. They were surprisingly reluctant to catch fire!
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© 2001 The Ministry of Defence
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Arnold, L., Pyne, K. (2001). Mission Accomplished — Grapple Z. In: Britain and the H-Bomb. Palgrave Macmillan, London. https://doi.org/10.1057/9780230599772_13
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DOI: https://doi.org/10.1057/9780230599772_13
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