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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 (240 km) in good visibility. From 1974 AWDREY units were used together with a device known as DIADEM (Direction
Indicator of Atomic Detonation by Electronic Means) which measured the
104:) operated by recording the peak overpressure of the blast wave from any nearby nuclear explosion. Any ultra-high-altitude nuclear explosion, designed to knock out the UK's communications and electronic equipment would not produce a detectable blast wave, and the AWDREY system was therefore the only method of identifying these bursts.
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With the display unit mounted in a 3-foot-high (0.91 m) 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
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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
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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
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nuclear weapon trials, after being mounted on board a ship. Although a single AWDREY unit could not differentiate between a nuclear explosion and a lightning strike, the units were installed sufficiently far apart that a lightning strike would not simultaneously register on two adjacent AWDREYs.
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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.
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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
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AWDREY was the principal method by which the UKWMO would achieve its second responsibility. Simultaneous responses on two or more AWDREY units would identify the explosion as a nuclear strike.
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54:(EMP) generated by an explosion. The instruments were in constant operation (state of readiness) between 1968 and 1992 and tested daily by full-time ROC officers.
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nuclear bursts within the attack, and the readings from ROC posts became the main method of detecting and identifying any subsequent near ground bursts.
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149:. The message would also include the three-letter group identifier, followed by the time and yield reading from the AWDREY printout. E.g.
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70:. The design was tested for performance and accuracy using real nuclear explosions at the 1957
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Royal
Observer Corps reports following a reading on AWDREY were prefixed with the codeword
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a lightning storm would be unlikely to trigger simultaneous AWDREY responses at two sites.
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was a desk-mounted automatic detection instrument, located at 12 of the 25
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English
Heritage, Swindon, 2003 revised 2004 (p.191 & 193)
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Atomic
Weapons Detection Recognition and Estimation of Yield
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A photograph of an AWDREY display unit taken in situ at the
82:(UKWMO), for whom the ROC provided the field force were:
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Cold War: Building for
Nuclear Confrontation 1946-1989
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English
Heritage, Swindon, 2003 revised 2004 (p.191-2)
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Cold War: Building for
Nuclear Confrontation 1946-1989
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Cold War: Building for Nuclear Confrontation 1946-1989
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English Heritage, Swindon, 2003 revised 2004 (p.187)
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Operational instruments of the Royal Observer Corps
173:United Kingdom Warning and Monitoring Organisation
93:Providing confirmation of nuclear strike on the UK
80:United Kingdom Warning and Monitoring Organisation
263:Cold War military equipment of the United Kingdom
62:AWDREY was designed, built and maintained by the
151:"TOCSIN BANG – CAR – 11.06 (hours) – 3 megatons"
78:The first two primary responsibilities of the
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212:"U.K.W.M.O. Group and Sector Headquarters"
124:Awdrey Timing and Logic on display in York
86:Warning the public of any air attack (see
153:(with CAR relating to Carlisle control).
100:ROC post bomb detection instruments (see
237:COCROFT, Wayne D and THOMAS, Roger J C
224:COCROFT, Wayne D and THOMAS, Roger J C
197:COCROFT, Wayne D and THOMAS, Roger J C
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72:Kiritimati (or Christmas Island)
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64:Atomic Weapons Establishment
38:(ROC) controls, across the
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52:electromagnetic pulse
30:known by the acronym
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258:Royal Observer Corps
163:Royal Observer Corps
102:Bomb Power Indicator
36:Royal Observer Corps
22:York Cold War Bunker
88:four-minute warning
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252:Categories
185:References
58:Operations
157:See also
141:Codeword
44:Cold War
32:AWDREY
66:at
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90:)
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