The Area

     All previous British atomic tests have taken place in Australia, either at Maralinga, in the South Australian desert, or in the small uninhabited Montebello Islands off the north-west coast. However, for testing weapons of the scope involved in Operation Grapple there could be no question, from the safety point of view, of using these continental proving grounds. Therefore, a completely new base had to be found which would conform to certain essentials. The base had to be remote from any inhabited area; have favourable wind and weather conditions for air and sea operations; be accessible (even if distant) from a source of supply, and have a suitable harbour for landing these supplies; and finally, be suitable for the construction of an airstrip which could be used by Valiants and other large aircraft.
      An area in the Pacific seemed to be the inevitable choice and after careful consideration, and in the light of surveys made by a ship of the Royal New Zealand Navy and by aircraft of the R.A.F., Christmas Island was selected as the base island and Malden Island as the instrumentation island.
     Christmas Island, a part of what are known collectively as the Northern Line islands, is the largest coral atoll in the Pacific, although its dimensions are only about 35 miles east and west by 24 miles at its greatest width. As you can see from the map, the shape of the island roughly resembles a large lobster claw, the jaws of which, opening to the northwest, contain a spacious and almost semi-circular lagoon. In general the elevation is only about 10 feet above sea-level, but to the east there are sand dunes rising to 20, and in some places to 40 feet. Surrounding the island is a fringing reef, several hundred yards in width. There are coconut palms and bush in the west, but merely a tough prickly grass (unsuitable for cattle) and low shrubs in the centre, the eastern part being largely bare. The climate does not encourage the growth of vegetation as the island is subject to severe droughts which may last many months. At such times only 6 inches of rain may fall in the whole year, but in other years over 100 inches have been recorded. Day temperatures vary between 70 and 100F, but the Easterly Trade Winds exert a cooling influence so that, despite the high humidity, the heat is not oppressive. No hurricanes have ever been experienced in the area.
    Beneath the Central Pacific lies a system of alternative ridges and troughs most of which trend from NW to SE. These ridges are really submarine mountains rising from the bottom of the ocean. Where they emerge above the surface they form volcanic islands, like the Hawaii