page_title: Atomic Weapons Detection Recognition and Estimation of Yield
section_title: Installation
hierarchical_section_title: Atomic Weapons Detection Recognition and Estimation of Yield / Installation
caption_attribution_description: English: Awdrey Logic and Timing cycle on display at the York site.
context_page_description: Atomic Weapons Detection Recognition and Estimation of Yield known by the acronym AWDREY was a desk-mounted automatic detection instrument, located at 12 of the 25 Royal Observer Corps controls, across the United Kingdom, during the Cold War. The instruments would have detected any nuclear explosions and indicated the estimated size in megatons.
  With the display unit mounted in a 3-foot-high steel cabinet, the system used two sets of five photo-sensitive cells within the detection head to record the intense flash of light produced by the detonation of the weapon followed, within a second, by a second intense flash. This double flash is characteristic of a nuclear explosion and measurement of the short gap between the two flashes enabled the weapon's power to be estimated, and the bearing to be indicated. It had a range of 150 miles in good visibility. From 1974 AWDREY units were used together with a device known as DIADEM which measured the electromagnetic pulse generated by an explosion. The instruments were in constant operation between 1968 and 1992 and tested daily by full-time ROC officers.
context_section_description: The AWDREY installation consisted of three separate elements: the sensor, the detection unit and the display cabinet (timer). The sensor was mounted on the roof of the building. The detection unit was installed in a special room that was enclosed inside a Faraday cage; in the case of the Royal Observer Corps controls, this was the "Radio Room" that already protected the sensitive radio equipment from the effects of EMP.
  The display unit (timer) (shown in the photograph above) could be mounted anywhere in the building – at ROC controls this was usually on the balcony adjacent to the Triangulation Team. The three elements of the installation were connected by EMP-shielded and heavy duty cabling.
  During the early phase of operations, a spare observer was required to stand next to the display unit and monitor it constantly to identify initial responses. Once a nuclear strike on the UK had been confirmed by the Director UKWMO (or his deputy), readings from AWDREY were ignored during subsequent nuclear bursts within the attack, and the readings from ROC posts became the main method of detecting and identifying any subsequent near ground bursts.
  The 12 ROC AWDREY units were located at the group controls in Exeter, Oxford, Horsham, Bristol, Colchester, Carmarthen, Coventry, Carlisle, York, Dundee, Inverness and Belfast.  This siting pattern provided sufficient detectors that the entire UK was covered, but the units were far enough apart that a lightning storm would be unlikely to trigger simultaneous AWDREY responses at two sites.
caption: Awdrey Timing and Logic on display in York
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