Royal Observer Corps Post Equipment
ROC posts were provided with a range of equipment to fulfill a wide range of requirements, first there was the need for personnel to live below ground for a period immediately following a nuclear attack, this was estimated to be between two and three weeks. Sanitation was provided by an Elsan chemical toilet housed in the lower part of the entrance shaft. For sleeping a two tier bunk was located at the further end from the entrance. Cooking was done on a small solid fuel burner, and had to be done outside of the post. Water was stored in jerrycans. As far as comfort was concerned that was about it, other than some folding chairs. A small kit of tools was also provided to perform key functions such as mounting monitoring equipment, maintaining the generator and digging holes.There was also the need for performing the primary function of the post, that is monitoring explosions and tracking radiation. The information gathered had to be communicated to the outside world, and so all posts had dedicated line communications, and one in every small cluster of 2-4 posts had a vhf radio transceiver, such posts were defined as master posts.
Some posts had an additional responsibility of reporting basic meteorological information, for this purpose they had a couple of extra devices mentioned below.
RADIAC equipment
All posts were equipped with RADIAC equipment, this is described on the Radiac Equipment page. Initially this comprised personal dosimeters together with a charger, a survey meter and a Fixed Survey meter or FSM. In the mid 1960s the Meter Survey RADIAC was replaced with the lightweight survey meter. In 1982/83 this was again replaced, this time with the PDRM82. The FSM was replaced with the PDRM82F at about the same time, although training materials still referred to this as the FSM.Bomb Power Indicator (BPI)
Provided that the distance from ground
zero is known, the power of a nuclear weapon can be calculated from the
peak-overpressure produced by the blast wave. The Bomb Power Indicator
(BPI) was designed to record this pressure.The BPI comprises a metal bellows, rather like an aneroid barometer, one side of which is exposed to atmospheric pressure. Attached to the bellows is a push rod which bears against a lever fixed to a spindle. A pointer attached to the spindle moves across a scale reading from 0 to 50 kilopascals (kPa). Originally instruments were calibrated from 0 to 5 pounds per square inch (psi). Above ground a pair of circular baffle plates, six inches in diameter and separated by 1/2", protect the opening of the pipe which is connected to the gauge below ground in the protected monitoring post. The baffles were normally stored below ground and only screwed onto the top of the pipe at the start of exercises or at Transition To War. Outside of operations the BPI pipe was protected by a screw on cap and there was a drain valve at the base of the instrument to remove any excess rainwater.
If the BPI registered a reading of 0.3 p.s.i. or 2kPa, or higher, the operator would wait ten seconds before pressing the reset button and recording the reading prior to making an immediate report to the group control, in the form "Tocsin - Horsham 10 post - oh nine thirty five - pressure three point four, over." One minute after a BPI reading an observer would be sent above ground to change the photographic papers in the Ground Zero Indicator.
Ground Zero Indicator (GZI)
The GZI consisted of four horizontally
mounted pinhole cameras each facing a cardinal compass point within a
white enameled metal drum, each 'camera' contained a sheet of
photosensitive paper mounted within a clear plastic cassette. The
cassettes were positioned such that each pointed to a cardinal compass
point, with a small overlap between each field of view. The cassette
graticule was marked in five degree intervals in both elevation and
azimuth. The vertical or elevation markings were from 15° below the
horizon to 45° above. Each graticule was also marked with the cardinal
compass point (N,E,S,W) against the central line running down the
cassette. The limits of azimuth (bearing) were: N (North) 305° to 55°; E
(East) 35° to 145°; S South) 125° to 235° and W (West) 215° to 325°.The bright flash from a nuclear explosion would produce a mark on one or two of the papers within the drum. The position of the spot enabled the bearing and elevatio
The altitude of the explosion was important because a ground or near ground burst would produce high levels of radioactive fallout, whereas an air burst would produce large distance and short lived initial radiations but relatively little fallout. Once combined with the peak-overpressure readings from post Bomb Power Indicator readings the power of the burst in megatons could also be calculated by the Triangulation Team in the group control building, using a hand held plastic calculator device.
When not in use the GZI was stored below ground. Upon manning up the post, the GZI was mounted on a domed plate affixed to the top of the access shaft. Three nuts were used, and the studs in the base of the GZI and the matching holes in the base were spaced in such a way that the instrument could only be fitted in one orientation. The orientation was determined during the installation of the mounting.
The post toolkit included a spanner for fitting the GZI to the mount, the opposite end of the spanner was of a larger size and became obsolete by the time the GZI was brought into general use, that end was for removing the cover. The later GZI had a hand operated release.
Changing GZI Papers
GZI papers were changed according to a routin based upon the time of year. In summer (21st March - 21st September) papers were changed twice a day, at noon and just after sunset. In winter on odd numbered dates only, just after sunset.
At posts the instruction to change papers,
given by the No 1 observer, whether in response to a nuclear burst or
otherwise, meant that the No 3 observer left the post, carrying the new
papers in a light-proof satchel. No 3 would remove the top of the GZI,
remove the cassettes and place them in the satchel. They would then
insert the new cassettes in sequence and replace the lid.The observer next returned to the observation room, if fallout had already arrived then they needed to decontaminate, but not before passing the exposed cassettes to the observer who assessed the papers. Assessment is too complex to go into here, but broadly the azimuth and elevation of the centre of any spots, whether or not a spot touches the horizon and the spot size were all determined prior to sending the report, this is given in the form below, in the case of a spot touching the horizon line, or if the horizon line is not visible, the 0° elevation line, then the word "clear" would be replaced by "touching".
The report to Group, of the GZI paper shown would be in the form: "Nuclear burst, Horsham ten post over." - Plotter responds, "Horsham ten post over." "Twelve sixteen - bearing zero six five - elevation two one - clear - spot size zero seven - over." Plotter responds; "Thank you, out."
The Bomb Power Indicator and Ground Zero Indicator
This
video is provided by the Imperial War Museum© under the terms of
a non-commercial licence.
Communications
Telephone Observer AD 163
Until the early 1960s, in its nuclear reporting role, the ROC used the AD63 headset telephone to give voice communication with ROC Group HQ over a private telephone circuit shared with other members of a cluster. The AD 163 used magneto ringing and a battery for the speech circuit. This instrument had been in use during World War II.Teletalk Unit AD 3460
In the early 1960s the AD 163 was replaced with the Teletalk Unit AD 3460. This used two batteries, 67.5 volts for the calling or signalling circuit, and 6 volts for speech. The loudspeaker also functioned as the microphone. The volume control on the left also switched the unit on and off. The lever switch on the right was biased to the centre receive position. In the upwards direction the switch sent the call signal. Depressing the switch gave a press-to-talk (prestel) function. The telephone circuit was shared with the WB400A warning receiver, this necessitated the inclusion of a filter to remove the 72kHz carrier frequency from the latter's signal.
Loudspeaker Telephone AD8010
The Loudspeaker Telephone AD8010 aka
"Teletalk" was introduced into posts in 1964. An early tele-talk was a
small grey box that was approximately 20cm x 20cm and contained a
microphone and amplifier very similar to a telephone. The later
tele-talk was of a bright blue and yellow 'clam-shell' design and was
introduced circa 1982. Both versions were line powered and
therefore required no batteries or mains power connections. All that was
required was therefore a standard telephone line accessing into the
monitoring post. 
WB400A
Carrier Receiver
Operationally during the Cold War the
Director UKWMO would have been located at the United Kingdom Regional
Air Operations Command (UK RAOC) within Strike Command's Operations
Centre nuclear bunker at RAF High Wycombe to instigate the national air
raid warnings, with the Deputy Director located at a standby UK RAOC, at
Goosnargh near Preston within the UKWMO Western Sector nuclear bunker.
Warnings were instantly distributed around the country by the HANDEL
Warning Broadcast System via 250 Carrier Control Points located at major
police headquarters thence to 1700 Carrier Receivers, initially the
WB400A, but later the WB1400, located in selected buildings such as
schools, hospitals, police stations, public houses, even occasionally a
private house and at ROC posts.BT communications board
This board holds the WB1401 Carrier
Receiver and associated equipment. The WB1401 replaced the
WB400 Carrier Receiver, but used the same 72kHz carrier system.The BT telephone line was connected at the Block Terminal BT 52A, this was in turn connected to the Filter Unit WB1401, from there to the Receiver Speech WB1401, and finally to the Loudspeaker Unit WB1401. Layouts of these boards varied somewhat over the years, and upon the GPO engineers that installed them! It is even suggested that it depended to some extent on what they had in their van.
BE525 Post Radio
Master Posts were equipped with VHF transceivers. Initially these were ATE Countryman single channel VHF radios. These early valve sets were not successful, and were replaced in the mid 1980s by
fully transistorised sets operating in the frequency band 80.000-81.500
MHz. They were three channel FM sets built by Burndept, model No BE525.
The antenna was external and fitted to a pneumatic mast.
