Bomb Power Indicator known by the acronym BPI was a detection instrument, located at the twenty five

British British may refer to: Peoples, culture, and language * British people, nationals or natives of the United Kingdom, British Overseas Territories, and Crown Dependencies. ** Britishness, the British identity and common culture * British English, ...

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 ...

controls and nearly 1,500 ROC underground monitoring posts, across the United Kingdom, 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 ...

that would have detected any nuclear explosions and measured the peak-overpressure of the blast waves.

Overview

The instruments, operated by volunteers, measured the level of peak-overpressure at the instrument's location. Once readings had been combined with information provided by 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 ...

s it would be possible to estimate the size of the nuclear explosion in megatons. Detailed BPI information was backed up by the automatic

AWDREY 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 War ...

readings. The BPI 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 ...

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, Basingsto ...

. The design was tested for performance and accuracy using real nuclear explosions at the 1957 Kiritimati (or Christmas Island) nuclear weapons tests, after being mounted on board a ship. A number of BPIs were also tested in Australia during the Operation Buffalo series of nuclear tests, with units located at various distances from

ground zero In relation to nuclear explosions and other large bombs, ground zero (also called surface zero) is the point on the Earth's surface closest to a detonation. In the case of an explosion above the ground, ''ground zero'' is the point on the ground ...

Operations

Above ground a pair of circular plated baffles would be affected by the passing of the blast wave. The detector was connected by a steel pipe to the indicator dial below ground in the protected monitoring post. The dial was wall mounted and measured readings from 0.1 to 5 pounds per square inch peak overpressure. Readings below 0.3 pounds per square inch were noted but not reported. 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 or higher the operator would wait ten seconds before pressing the reset button and making a report to the group control. One minute after a BPI reading an observer is sent above ground to change the photographic papers in the

Codeword

Royal Observer Corps reports following a reading on any BPI were prefixed with the codeword "Tocsin" e.g. "Tocsin Shrewsbury 56 post - (time) oh five fifty five - pressure two point six".

References

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Overview

Operations

Codeword

References

See also