NS4079 : Alexandria ROC Bunker: GZI mount

taken 8 years ago, near to Bonhill, West Dunbartonshire, Great Britain

Alexandria ROC Bunker: GZI mount
Alexandria ROC Bunker: GZI mount
See NS4079 : Royal Observer Corps Monitoring Post, Alexandria and NS4079 : Royal Observer Corps Monitoring Post, Alexandria for context, and for a view of the whole structure.

The access shaft can be seen on the right. The mounting plate near the centre of the photograph would have supported the Ground Zero Indicator (GZI), which would have operated rather like a sunshine recorder, but with pinholes and photosensitive paper, to determine the direction and elevation of nuclear blasts.
Alexandria ROC Bunker

This ROC monitoring post see Link and Link for a detailed description of these Cold War relics was a master post. It is set in a field, on a west-facing slope, just downhill from a small square of woodland that contains the ruins of Northfield Cottage. At the foot of the slope is Northfield Road and the Dalmonach estate.

ROC monitoring post

The Royal Observer corps was a civil defence organisation operating in the United Kingdom between 29 October 1925 and 31 December 1995.

During the cold war ROC monitoring posts were developed for monitoring fallout and radiation in the event of a nuclear attack. The operators hidden below would occasionally emerge to collected photographic film from a 4-axis parabolic camera mounted near the hatch, retreating below ground to develop it. A patch of darkening might have indicated the direction of an explosion. Once centally collated these observations would triangulate the site of an attack.

A variety of instruments would detect radiation and fallout levels, and the bunker itself used the earth to protect the volunteer observers, who had telephone and radio communications up the chain of command.

There were 1,563 of these posts constructed and one of the specialist groups researching the history of the ROC has mapped them all. See LinkExternal link (there is a great deal of detailed information about the posts on the rest of that site)

See LinkExternal link for background and a reconstruction of a working observation post.

There is a good history of the ROC on wikipedia at LinkExternal link and a charitable association for the welfare of the former volunteers at LinkExternal link

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NS4079, 79 images   (more nearby search)
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Date Taken
Monday, 25 June, 2012   (more nearby)
Sunday, 8 July, 2012
Geographical Context
Derelict, Disused  Defence, Military 
Subject Location
OSGB36: geotagged! NS 4052 7993 [10m precision]
WGS84: 55:59.1455N 4:33.4781W
Camera Location
OSGB36: geotagged! NS 4052 7993
View Direction
South-southwest (about 202 degrees)
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Royal Observer Corps 

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