As part of Heritage Open Days 2008, Mapping Kent joined joined landscape investigator, Mark Harrison and over twenty enthusiasts in a fascinating tour of Kent’s involvement in the conflicts experienced in the 19th and 20th centuries.

From a panoramic position situated at Victory Wood near Whitstable, participants gained a unique insight into the construction of Nelson’s Fleet; the development of Second World War RADAR and anti-invasion defences and the threat posed to Britain during the Cold War.

The group was joined by Ant Larkins, who, as a member of the Royal Observer Corps (ROC) was deployed to the observation post. Ant was able to provide a unique insight into the role of the ROC and the living conditions experienced by the observers.

The Royal Observer Corps was a voluntary organisation, entrusted with the task of monitoring and recording a nuclear attack on the UK. It was the Corp's role job to monitor the number of bombs falling, where they might land, and to track the radioactive fallout thrown up by any localised explosions. The underground post consisted of a 15ft entrance shaft which gave access to two rooms, one containing a chemical toilet and a monitoring room furnished with canvas chairs, folding table, shelving, cupboards and a set of bunk beds. A ventilation shaft with two louvered vents was located alongside the entrance shaft with a second air shaft at the other end of the room. Lighting was provided by a 12 volt battery located behind the monitoring room door.

Each bunker was staffed by three volunteers equipped with an array of monitoring equipment designed to measure the detonation power, the movement of radioactive fallout and to warn the public of an imminent attack, or approaching fallout. Communications between posts and Group HQ's was by GPO telephone lines (A line of telegraph poles half way across a field are often still visible and give the site away) and in 1964 the conventional headset and microphone was replaced by 'Tele-talk' an 8 inch square box containing microphone and amplifier. In case of emergencies, all Group HQ's and one post in each cluster were equipped with VHF radios and radio masts, these posts being known as master posts.

The bunkers were only intended to be manned for a total of two weeks. Following re-organisation of Britain's defence systems during the 1960s some bunkers were closed, and in 1991 it was decided that the ROC would cease active training and the remaining underground posts were closed.

The monitoring function is now undertaken by electronic sensors that can automatically detect and pinpoint any missile threat and monitor fallout and radiation levels.

The ROC bunker located at Clay Hill, Denstroude was constructed in 1966 and closed in 1976.The bunker has been cleared of all equipment and is now owned by the Woodland Trust.

Instrumentation:

Atomic Weapons Detection Recognition and Estimation of Yield - AWDREY

A desk mounted automatic instrument, located at controls, that detected nuclear explosions and indicated the estimated size in megatons. Operating by measuring the level of electro magnetic pulse (EMP) the instruments were tested daily by wholetime ROC officers and regularly reacted to the EMP from lightning strikes during thunderstorms

Bomb Power Indicator - BPI

Consisted of a peak overpressure gauge with a dial that would register when the pressure wave from a nuclear explosion passed over the post. When related to the distance of the explosion from the post this pressure would indicate the power of the explosion. The Bomb Power Indicator consisted of a baffle plate mounted on a steel pipe at the surface. At the base of the pipe, situated in the monitoring room, was an indicator unit fitted with bellows connected to a dial. The air over-pressure from the blast would pass down the pipe to the bellows where the pressure of the blast would be indicated.

Ground Zero Indicator - GZI

Also known as a shadowgraph consisted of four horizontally mounted cardinal compass point pinhole cameras within a metal drum, each 'camera' contained a sheet of photosensitive paper on which were printed horizontal and vertical calibration lines. The flash from a nuclear explosion would produce a mark on one or two of the papers within the drum. The position of the mark enabled the bearing and height of the burst to be estimated. With triangulation between neighbouring posts these readings would give an accurate height and position. The altitude of the explosion was important because a ground or near ground burst would produce radioactive fallout, whereas an air burst would produce only short distance and short lived initial radiations, but no fallout. The GZI was mounted on a convex metal plate, usually located on top of the vent shaft next to the entrance but it necessitated somebody emerging into the open air to retrieve the sheets of photographic paper.

Measurement of ionising radiation

The Radiac Survey Meter No 2 - RSM A 1955 meter which counted the particles produced by radioactive decay. This meter was superseded in 1958 by the Fixed Survey Meter - FSM. The RSM was retained for post attack mobile monitoring missions.

Fixed Survey Meter - FSM

Introduced in 1958, The indicator unit was mounted on the table and connected to the surface by cable running through a pipe on the end of which was fitted the ionization chamber. The FSM could be operated from within the post with a cable leading to the detector mounted externally and protected by a polycarbinate domeand could read up to 500 roentgens per hour increasing to more than 5000 R/hr if the ionization chamber was withdrawn down the pipe.

Dosimeter

Pocket meters were issued to individual observers for measuring their personal levels of radiation absorption during operations.

Mapping Kent would like to thank Mark Harrison for contributing this article