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Royal Observer Corps The Royal Observer Corps (ROC) was a civil defence organisation intended for the visual detection, identification, tracking and reporting of aircraft over Great Britain. It operated in the United Kingdom between 29 October 1925 and 31 December ...
(ROC) was a
civil defence Civil defense ( en, region=gb, civil defence) or civil protection is an effort to protect the citizens of a state (generally non-combatants) from man-made and natural disasters. It uses the principles of emergency operations: prevention, mit ...
organisation operating in the
United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the continental mainland. It comprises England, Scotland, Wales and North ...
between October 1925 and 31 December 1995, when the Corps' civilian volunteers were stood down. (ROC headquarters staff at
RAF Bentley Priory RAF Bentley Priory was a non-flying Royal Air Force station near Stanmore in the London Borough of Harrow. It was the headquarters of Fighter Command in the Battle of Britain and throughout the Second World War. During the war, two enemy bomb ...
stood down on 31 March 1996). Composed mainly of civilian spare-time volunteers, ROC personnel wore a
Royal Air Force The Royal Air Force (RAF) is the United Kingdom's air and space force. It was formed towards the end of the First World War on 1 April 1918, becoming the first independent air force in the world, by regrouping the Royal Flying Corps (RFC) and ...
(RAF) style uniform and latterly came under the administrative control of
RAF Strike Command The Royal Air Force's Strike Command was the military formation which controlled the majority of the United Kingdom's bomber and fighter aircraft from 1968 until 2007 when it merged with Personnel and Training Command to form the single Air C ...
and the operational control of the Home Office. Civilian volunteers were trained and administered by a small
cadre Cadre may refer to: *Cadre (military), a group of officers or NCOs around whom a unit is formed, or a training staff *Cadre (politics), a politically controlled appointment to an institution in order to circumvent the state and bring control to th ...
of professional full-time officers under the command of the
Commandant Royal Observer Corps The Commandant of the Royal Observer Corps (CROC) was the Royal Air Force commander of the Royal Observer Corps. All the holders of the post were RAF officers in the rank of Air Commodore, initially retired reserve officers then Auxiliary offic ...
; a serving RAF Air Commodore. This sub article lists and describes the instruments used by the ROC in their nuclear detection and reporting role during the
Cold War The Cold War is a term commonly used to refer to a period of geopolitical tension between the United States and the Soviet Union and their respective allies, the Western Bloc and the Eastern Bloc. The term '' cold war'' is used because the ...
period. __TOC__


Initial detection of nuclear bursts on the UK

Atomic Weapons Detection Recognition and Estimation of Yield Atomic Weapons Detection Recognition and Estimation of Yield known by the acronym AWDREY was a desk-mounted automatic detection instrument, located at 12 of the 25 Royal Observer Corps (ROC) controls, across the United Kingdom, during the Cold ...
known as AWDREY was a desk mounted automatic instrument, located at controls, that detected nuclear explosions and indicated the estimated size in megatons. Operating by measuring the intense flashes emitted by a nuclear explosion, together with a unit known as DIADEM which measured Electromagnetic Pulse (EMP), the instruments were tested daily by wholetime ROC officers and regularly reacted to the EMP from lightning strikes during thunderstorms.AWDREY and other instruments can be seen here
/ref> AWDREY was designed and built by the
Atomic Weapons Establishment The Atomic Weapons Establishment (AWE) is a United Kingdom Ministry of Defence research facility responsible for the design, manufacture and support of warheads for the UK's nuclear weapons. It is the successor to the Atomic Weapons Research ...
at
Aldermaston Aldermaston is a village and civil parish in Berkshire, England. In the 2011 Census, the parish had a population of 1015. The village is in the Kennet Valley and bounds Hampshire to the south. It is approximately from Newbury, Basingstoke ...
and tested for performance and accuracy on real nuclear explosions at the 1957 Kiritimati (or Christmas Island) nuclear bomb test (after being mounted on board a ship). Reports following a reading on AWDREY were prefixed with the codewords "Tocsin Bang". The
Bomb Power Indicator Bomb Power Indicator known by the acronym BPI was a detection instrument, located at the twenty five British Royal Observer Corps controls and nearly 1,500 ROC underground monitoring posts, across the United Kingdom, during the Cold War that would ...
or 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. Reports following a reading on the BPI were preceded by the codeword "Tocsin". The
Ground Zero Indicator Ground may refer to: Geology * Land, the surface of the Earth not covered by water * Soil, a mixture of clay, sand and organic matter present on the surface of the Earth Electricity * Ground (electricity), the reference point in an electrical c ...
, or GZI or
shadowgraph Shadowgraph is an optical method that reveals non-uniformities in transparent media like air, water, or glass. It is related to, but simpler than, the schlieren and schlieren photography methods that perform a similar function. Shadowgraph is a ty ...
, consisted of four horizontally mounted cardinal compass point
pinhole camera A pinhole camera is a simple camera without a lens but with a tiny aperture (the so-called ''pinhole'')—effectively a light-proof box with a small hole in one side. Light from a scene passes through the aperture and projects an inverted image o ...
s within a metal drum, each 'camera' contained a sheet of
photosensitive Photosensitivity is the amount to which an object reacts upon receiving photons, especially visible light. In medicine, the term is principally used for abnormal reactions of the skin, and two types are distinguished, photoallergy and phototoxicity. ...
paper on which were printed horizontal and vertical calibration lines. The flash from a
nuclear explosion A nuclear explosion is an explosion that occurs as a result of the rapid release of energy from a high-speed nuclear reaction. The driving reaction may be nuclear fission or nuclear fusion or a multi-stage cascading combination of the two, t ...
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).


Static measurement of ionising radiation

The Radiac Survey Meter No 2 or RSM was a 1955-meter which used an ionisation chamber to measure gamma radiation, it could measure beta, by removing the base-plate and opening the beta shield. This meter suffered from a number of disadvantages: it required three different types of batteries, of which two were obsolete and had to be manufactured to special order, the circuit included a single electrometer valve or tube. These were favored as they had been tested on fallout in Australia after the Operation Buffalo nuclear tests, and remained in use until 1982 by commissioning a manufacturer to regularly produce special production runs of the obsolete batteries. Within the ROC the RSM was only used at post sites for three years when it was superseded in 1958 by the FSM and the RSM retained only for post attack mobile monitoring missions. The
Fixed Survey Meter The Fixed Survey Meter was a specialist detection instrument used by the Royal Observer Corps during the Cold War between 1958 and 1982 to detect ionising radiation from nuclear fallout generated by a ground burst. Overview Fixed Survey Meter The ...
or FSM was introduced in 1958. For the first time it was possible to operate the unit from within the Monitoring Post or Group HQ using an external Geiger Muller Probe connected via coaxial cable and mounted to a telescopic rod and protected on the surface by a polycarbonate dome. The FSM used the same obsolete high voltage batteries as the RSM. In 1985 this instrument was replaced by the PDRM82(F). The PDRM82(F) was the fixed desktop version of the PDRM82. It gave more accurate readings and used standard 'C' cell torch batteries that lasted many times longer, up to 400 hours of operation. The compact and robust instruments were housed in sturdy orange coloured polycarbonate cases and had clear liquid crystal displays. The PDRM82(F) could also be operated from within the Monitoring Post or Group HQ as before, using an external Geiger Muller Probe connected via coaxial cable. The telescopic rod, mounting bracket and polycarbonate dome used by the earlier FSM remained in service and continued to be used with the PDRM82(F).


Portable measurement of radiation during Mobile Monitoring missions

The Radiac Survey Meter No 2 or RSM was a 1955-meter which measured gamma and beta radiation. Having been superseded within the ROC by the Fixed Survey Meter the RSM remained in use only for post attack mobile monitoring missions in a post attack period. Image can be seen in ‘Static measurement of ionising radiation’ section. The Radiac Survey Meter, Lightweight, MkVI, produced by the AVO company (The MkIII and MkIV were also available) were issued to the ROC in the mid-late 1960s, but were not regarded favourable due to using almost obsolete Mallory batteries and were ionisation type meters that measured gamma radiation. The
PDRM82 This article is about Geiger counters and ion-chamber instruments, and it uses the term "Geiger counter" as a colloquial name for any hand-held radiation measuring device in civil defense. However, most civil defense devices were ion-chamber ra ...
or Portable Dose Rate Meter was the standard portable version of the new meters, that were manufactured by
Plessey The Plessey Company plc was a British electronics, defence and telecommunications company. It originated in 1917, growing and diversifying into electronics. It expanded after World War II by acquisition of companies and formed overseas compani ...
and introduced during the 1980s, giving more accurate readings and using standard 'C' cell torch batteries that lasted many times longer, up to 400 hours of operation. The compact and robust instruments were housed in sturdy orange coloured polycarbonate cases and had clear liquid crystal displays. The Radiac sensor was self-contained within the casing.


Measurement of personal absorptions

The
Dosimeter A radiation dosimeter is a device that measures dose uptake of external ionizing radiation. It is worn by the person being monitored when used as a personal dosimeter, and is a record of the radiation dose received. Modern electronic personal dos ...
pocket meters were issued to individual observers for measuring their personal levels of radiation absorption during operations. Three different grades of dosimeter were used, depending on ambient radiation levels. The original hand wound and temperamental dosimeter charging units (Charging Unit, Individual, Dosimeter No.1 & No.2) were replaced during the 1980s by a battery operated automatic charging unit (EAL Type N.105A).


See also

*
Royal Observer Corps The Royal Observer Corps (ROC) was a civil defence organisation intended for the visual detection, identification, tracking and reporting of aircraft over Great Britain. It operated in the United Kingdom between 29 October 1925 and 31 December ...
* Royal Observer Corps Monitoring Post *
Bomb Power Indicator Bomb Power Indicator known by the acronym BPI was a detection instrument, located at the twenty five British Royal Observer Corps controls and nearly 1,500 ROC underground monitoring posts, across the United Kingdom, during the Cold War that would ...
*
Ground Zero Indicator Ground may refer to: Geology * Land, the surface of the Earth not covered by water * Soil, a mixture of clay, sand and organic matter present on the surface of the Earth Electricity * Ground (electricity), the reference point in an electrical c ...
*
Fixed Survey Meter The Fixed Survey Meter was a specialist detection instrument used by the Royal Observer Corps during the Cold War between 1958 and 1982 to detect ionising radiation from nuclear fallout generated by a ground burst. Overview Fixed Survey Meter The ...
*
Nuclear MASINT Nuclear MASINT is one of the six major subdisciplines generally accepted to make up Measurement and Signature Intelligence (MASINT), which covers measurement and characterization of information derived from nuclear radiation and other physical phe ...
US equivalent


References

{{reflist *Operator's Handbook for Meter Survey Radiac No.2 Published A.E.R.E. 1955 *Civil Defence Pocket Book, General Information published Home Office (various dates) Royal Observer Corps Cold War military equipment of the United Kingdom Measuring instruments