Operational Equipment – Nuclear Role

In this section you will find information and photos of the most common operational equipment used by ROC personnel in the underground monitoring posts during the Cold War Nuclear role from 1956 to approx 1991.


The Bomb Power Indicator (BPI) was a device located at all group controls and all underground posts that was capable of measuring the peak over-pressure of a nuclear explosion. It was designed at the Atomic Weapons Research Establishment in Aldermaston and tested with live explosions at the Christmas Island Nuclear tests. It was designed to work in conjuncton with the GZI (below). It worked by diverting the over-pressure wave through a set of baffles and down a pipe to the gauge to give a reading originally in PSI, but after decimalisation in Kilopascals.


The Ground Zero Indicator (GZI) was a piece of equipment designed to triangulate the ‘ground zero’ of any nuclear blast. It has 4 faces, one for each cardinal point of the compass, which contain a low-light sensitivity photographic paper. Placed over these pieces of photographic paper were graticules calibrate with horizontal height lines and vertical bearing lines. The bright flash from a nuclear explosion would ‘mark’ the paper giving height and bearing – the information from 3 posts (a cluster) could be triangulated at group HQ to give the ground zero. When changing the photographic paper Observer would have placed new and exposed paper in a lightproof satchel in order to protect it from unnecessary light exposure, as a geeky side note we have so far found 4 different styles of lightproof satchel!


The fixed survey meter introduced in 1958 (FSM) was a piece of equipment designed at the Atomic Weapons Estrablishment and manufactured by Avo (of Avometers fame) to detect the ionising radiation from radioactive fallout following a nuclear strike. The original was quite a delicate piece of equipment and was kept in controlled conditions at Group HQ’s and would only issued in the run up to war. In order to faciliate training however, there was a Training version which operated using an acetate strip to move a needle in a clockwork ‘copy’ of the real FSM. This FSMT was robust enough to be used and kept in posts on a more regular basis. To see a stop/motion video of an FSM(T) in use click this link. FSM VIDEO

In the 1980’s the early FSM was withdrawn and replaced by a more modern PDRM82(f) which was a a digital meter, and as it was far more robust could be kept in posts almost indefinitely. A new ‘digital’ FSM trainer was introduced that used an EEPROM cartridge to feed the actual FSM simulated readings. This device was later modified with a small plastic tab as it became apparent that it could be inadvertently turned off during an exercise.  The display for both the early and later FSM was mounted on the desk, and, via a large flanged pipe in the ceiling, a probe was passed on a long pole to give the readings from outside the post. To prevent radioactive dust entering the post, or the probe being damaged by weather, the top of the flanged pipe had a polycarbonate dome to protect it. A short video if the Clockwork FSM running is available here: Clockwork FSMT

Portable Radiation Meters, Dosimeter Chargers and Dosimeter Pens

The Observers were issued portable Radiation Meters quite early on to provide a radiation detecting instrument to ‘bridge the gap’ while the FSM was undergoing development and testing. The first instrument the Corps were issued was the Radiac Survey Meter No2, a device introduced in 1955 and tested extensively during the Operation Buffalo nuclear tests in Australia where it was found to work effectively in the presence of radioactive fallout. It was powered by high voltage batteries, and was in use until 1982 for the mobile monitoring role at which point it was replaced by the Portable Dose Rate Meter 1982 (PDRM82) which was a portable version of the new FSM introduced at the same time.
To measure their personal exposure to radiation Observers were issued dosimeters and a dosimeter charger to read and reset them. A dosimeter works by measuring the rate of static discharge caused by a radiation field, this causes a hairline thread to move on a scale giving a reading of radiation dose. The original issue dosimeter charger worked by hand-winding a charging handle on the side to reset the dosimeter, and the dosimeter was read by either looking through it at a light source of by angling a mirror in the dosimeter charger to allow the scale to be read. These were somewhat temperamental to use and were also upgraded in the 1980’s to modern battery operated dosimeter chargers manufactured by EAL that were much easier and more accurate to use. Its worth noting for collectors that the ROC were not issued Stephen brand dosimeter chargers.


A petrol generator set rated at 12v and 300w was provided to the Posts to enable them to recharge the batteries that powered the lights and radio (if applicable). These were small single cylinder Villiers engines powering a dynamo. The PE sets were supplied by either  Swan of Southampton or AC Morrison of Oxfordshire and were essentially identical apart from minor changes to the carry frame (Swan is more square and chunky) and ancillary components such as the exhaust. It was planned in the late 1980’s to role out a 240v/12v generator manufactured by Yamaha but the stand-down of the Corps and closure of Posts occurred before these could be rolled out nationally. Click this link for  PDF of the Set instructions – pe_battery_charger


A radio set was supplied to Master Posts (1 post in each cluster was a master post) as insurance against telephone lines failing in the post-attack period. Two types of radio were issued, the original Plessey/AT+E countryman valve radio, and later 1980’s Burndept BE525 transistorised radio both types being VHF. The aerial mast was a pneumatically raised Clarke Mast mounted, in most cases, on the side of the ventilation shaft and controlled from inside the post by means of a hand pump to raise and lower it.


Introduced in the early 1960’s to replace the head and breast set magneto telephone, the ‘Units, Intercom LB AD 3460’ (teletalk) was a significant upgrade. Simpler to use and with no need to be ‘tied’ to the telephone by a cord it allowed the Observer to move around the underground post, unhindered. The speaker did double duty as both microphone and speaker. It was powered by a 6v and a 67.5v battery, a stock of which had to be kept in the post. It was normally in ‘receive’ mode and all calls in the cluster could be heard. The AD3460 was replaced in the early 1980’s with AD 8010 teletalk. This was essentially the same except it formed a ‘clamshell’ design and drew its power over the telephone lines from batteries at the exchange negating the need to keep a stock in the post. It was also smaller and had more advanced audio circuits (seperate speaker and mic) giving clearer sound. Originally it was not fitted with handles on the outside to open and close it, but it was soon realised that it sprung shut with some force so was modified with handles to allow safer opening and closing.

Fallout Warning Equipment

Posts were equipped with two pieces of equipment to warn the public of the arrival of radioactive fallout. The first was a hand cranked syren, of which there were 2 different designs and manufacturers. Carter and Secomak. The Secomak one is much more common. These are often passed off as ‘World War 2 air raid siren’ which is not true at all, as these weren’t introduced until post-WW2. It is easy to tell the difference, the Secomak has a rounded tubular frame and the Carter triangular frame, both styles were issued to the Corps. These ‘syrens’ were used to sound:

– ‘Red Warning’ – the imminent arrival of fallout (rising and falling tone for one minute)

– ‘Grey Warning’ – the arrival of fallout in one hour (constant alternating on and off every five turns via the shutter for two and a half minutes). This ‘Grey Warning’ was later dropped in the 1960’s to simplify the siren sounds and prevent confusion.

– ‘White Warning’ and the ‘all clear’ warning (constant tone for one minute)and a set of pyrotechnic maroons

The Posts were also issued with Fallout Warning Maroons – a pyrotechnic rocket that fired a burst up into the sky, detonating with a loud bang and a puff of black smoke. This was to provide a secondary audible and visual warning in addition to the siren. These would have been fired on the receiving of the ‘Red Warning’ or ‘Fallout Warning Black’ or if the radiation detecting instruments detected a rise in radiation levels. These fallout warning maroons were not kept at the post, but would have been issued by the Police during the transition to war phase, and observers would then have collected them from their HQ. There was no training device for these early on, and enterprising observers made fake items to train with. In the 1980s Paynes Wessex were commissioned to produce a new maroon launcher, and trainer. The trainer was powered by a battery and visually identical to the real thing except that it lit 3 lights in turn and beeped when the fire button was depressed.

WB400 and WB1400/1401 Carrier Receiver – ‘4 Minute Warning’

These devices were part of the HANDEL Nuclear Attack Warning System  – commonly known as the ‘four minute warning’ – that would have been  activated from either the Air Defence Operations Centre (ADOC) in High Wycombe or the standby site at UKWMO headquarters in Preston in the event of a nuclear attack from the air. This system is complex, and beyond the scope of this website so is best understood by visiting Steve Scanlon’s excellent ‘RingBell’ site here: RINGBELL , however a brief overview is below.

The HANDEL system was designed to quickly broadcast a warning or attack alert out to thousands of Warning Points simultaneously. The first iteration of this system was the WB400a ‘Carrier Receiver’, introduced in 1962, which was a one-way speaker powered by a 6 volt battery and connected to the local exchange. This device, when on emitted a ‘confidence’ tick to indicate the system was operational. In the event of a warning or attack alert being broadcast the volume would increase automatically and the voice message from the local main police station, via the WB600 Carrier Control Point, would be played out. The system was overhauled in the early 1980’s and the upgraded WB1400/01 was introduced – this differed in that it was powered over the telephone lines rather than an internal battery and two different models were introduced. A version  with a ‘ruggedised’ speaker in a metal hermetically sealed case for use in ROC Posts and other ‘environmentally hostile’ situations and a plastic non-sealed version for use in gentler environments like offices etc. Visually they are very different. The system was used until 1992 when the UKWMO was disbanded and the system switched off. 

Sundry Items

Post were issued a variety of sundry items for use withing the post, some of these were for quite pratical purposes (hauling net for instance) and some where for crew comfort, often these items were used up until standdown, so its possible to find 1950’s dated tea pots, bowls, mugs and cutlery in posts,

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Unless stated otherwise all items are in TheTimeChamber personal collection

Modified: 7th Jul 2022