Eastchurch Roc Post, opened in 1961, was one of two on the Island with the second one being atop Furze Hill. Three people, who would have monitored the affect of a nuclear blast in the area, would have manned the posts. This is the only remaining post on the Island - it closed in 1991.
The primary role of the Royal Observer Corps was to identify enemy aircraft during the Second World War but at the beginning of the Cold War and with the increased threat of a nuclear attack in the 1950’s, their responsibilities were expanded to also report nuclear blasts and monitor fall-out. Due to this change in threat 1563 underground posts were built in Great Britain and Northern Ireland.
Each post consists of an access shaft of around 15ft, two rooms, one being a small room with a chemical toilet and the second the monitoring room, which is usually 15’ by 7’ 6”. The monitoring room was fitted with bunk beds, cupboard, shelf, table and fold up chairs. There was a ventilation shaft with two louvered grilles near the entrance and another one at the opposite side of the room. A 12-volt battery usually found behind the monitoring room door provided lighting.
Equipment that could be found in each post consisted of the Fixed Survey Meter (FSM), the Bomb Power Indicator (BPI) and the Ground Zero Indicator (GZI). The Fixed Survey Meter, introduced in 1958, was mounted on the table and connected to the surface by a cable that ran through a pipe. At the end of the pipe an ionising chamber could be found .
The Bomb Power Indicator was introduced around the same time as the FSM, it consisted of a baffle surface plate mounted on a steel pipe at the surface. At the base of this pipe in the monitoring room was an indicator unit with bellows connected to a pointer. The air over-pressure from a blast would pass down the pipe to the bellows, the dial would then show the pressure of up to 5 PSI.
The Ground Zero Indicator consisted of a pinhole camera, the 4 pinholes faced the cardinal compass points and photographic paper was placed in front of each hole. In the event of a nuclear blast the image of the fireball would be captured by at least one of the pinholes and would aid in finding the size, height and location of each blast. The GZI was mounted on a convex metal plate, usually located on the vent shaft next to the entrance. The use of the GZI meant that one member of the post would have to leave the safety of the post to retrieve the photographic paper.
All posts were issued with hand-operated sirens, the ‘Secomak’ or ‘Carter’ was used for the red (attack) warning and also for the white (all clear) warning. The ‘maroon’ was used as the black warning (radioactive fallout), it was a sound flare and gave three loud bangs as a warning.
Communication between each post and group headquarters was by GPO telephone lines, these were replaces in 1964 by a TeleTalk. The TeleTalk was an 8” square box that contained a microphone and amplifier, in case of emergencies master posts, one post from a cluster of three, and the Group HQ’s had VHF radios and radio masts.