Tocsin Bang – The ROC

An ROC Post (Credit Nick Harding)An ROC Post (Credit Nick Harding)




The Royal Observer Corps was the UK’s prime resource for detecting and reporting on Nuclear Attacks on the UK. Its network of observation posts and regional headquarters formed the backbone of the UK Warning and Monitoring Organisation.

Initially formed in 1925 the ROC’s initial job was to spot enemy air attacks and during World War II it complemented the Chain Holme radar system and as a result it played a major part in the Battle of Britain.

Breifly stood down in 1945 following the end of the war it was re-activated in 1947 and adapted to take on its Cold War role. The UKWMO was formed 1957 and it was deemed that they would be the primary source of information to authorities during an attack with the ROC providing data on the location and power of nuclear weapons. The data suplied by the ROC would be used by the UKWMO to provide follow up information such as fallout warnings.

The UK was divided into sectors, Metropolitan, Midlands, Southern, Western and Caledonian with each having 5 sector control rooms. For Example Southern Sector had control rooms at Yeovil, Exeter, Bristol, Camarthen and Shrewsbury. In turn each control room had a network of Observation Posts in groups of 3 or 4. it is these posts that would detect and report initial explosion data and by using the data from several posts the control rooms could triangulate the location of the explosion. This, along with radiation reports from the posts, would allow the control rooms to disseminate accurate information for the UKWMO to report to the relevant authorities and issue accurate fallout warnings.

Observation posts would be manned by alternating crews of 4 or 5 ROC volunteers. They effectively live in the post for 12 hours at a time and sit there waiting for the balloon to go up. If a nuclear attack had taken place the BPI (bomb pressure indicator) would indicate this to the crew and it would be immediately reported using the codeword TOCSIN as a message such as “TOCSIN BRAVO TWO”. This message alerted control to the detonation. After a few minutes one member of the team would leave the post to collect the special photographic paper from the GZI (Ground Zero Indicator) which was effectively a pin hole camera. The flash from the detonation would burn a mark into the paper and using triangulation techniques, would reveal the location and altitude of the bomb. If this had happened it is likely that the crew on duty would be the last to ever man the post.

Once initial details are reported their job would then turn to monitoring for radioactive fallout which would then be reported to control at regular intervals.

The volunteers of the ROC stood ready day and night until they were officially stood down in 1991. Many of the posts and control rooms still exist today. One control at york (No20 Group Control) has been turned into a museum by English Heritage and some posts have been restored to allow visiting and education on their work. The nature of the work created strong bonds between members of the Royal Observer Corps and this is reflected by the existence of the Royal Observer Corps Association (ROCA)




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Britains Cold War
Consisting of historians, nuclear weapons and government planning experts Britain's Cold War provides news and information about The Cold War, Britain's Cold War and the new emerging Cold War often dubbed Cold War II. With more documents becoming declassified every day we learn a little bit more about what really went on between the end of World War II and the late 1990's.

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