DURING 1943-46, the Signals Research and Development Establishment operated a series of experimental centimetre-wave radio links along a 60-mile oversea path across Cardigan Bay. One major purpose of the investigation, which was carried out for an inter-Service committee under the chairmanship of Sir Edward Appleton, was to determine the degree to which meteorological factors affected microwave propagation and to find out to what extent the performance of such links could be predicted from synoptic data.