Atomic Weapons Detection Recognition and Estimation of Yield known by the accronym AWDREY was a desk mounted automatic detection instrument, located at the twenty five Royal Observer Corps controls, across the United Kingdom and Northern Ireland, during the Cold War that would have detected any nuclear explosions and indicated the estimated size in megatons.
The instrument operating by measuring the level of electro magnetic pulse (EMP) generated by any nuclear explosion. The instruments were in operation 24/7/365 between 1955 and 1992 and tested daily by wholetime ROC officers. AWDREY regularly reacted to the EMP from lightning strikes during thunderstorms. [1] Additional AWDREY instruments were also installed at each of the Regional Government Heaquarters (RGHQs) and at UKRAOC at RAF High Wycombe.
AWDREY was designed and built by the Atomic Weapons Establishment at Aldermaston and tested for performance and accuracy on real nuclear explosions at the 1957 Kiritimati (or Christmas Island) nuclear bomb test (after being mounted onboard a ship).
Codeword
Royal Observer Corps reports following a reading on AWDREY were prefixed with the codeword "TOCSIN BANG".