A matter of timing, October 1969–June 1970
The new degree of closeness exhibited in Anglo-American nuclear relations in the closing months of 1969 was given its most tangible form by the invitation that was extended in early October for potential British shielding materials to be included in the next series of US underground nuclear tests. Whether British knowledge derived from involvement in such underground nuclear experiments would have any practical application would, of course, depend on how successful the MoD's Central Scientific Staff were in selling the case for a Polaris improvement programme to higher political authority. For many senior Naval officers involved with the Polaris programme, exposure to the technical arguments and proposed solutions to the problem of overcoming ABM defences could not come a moment too soon. The start of British involvement with US underground flux tests was one of the immediate consequences of the important letter that John Foster had despatched to Cook in September 1969.