The Royal Observer Corps (ROC) was a civil defence organisation operating in the United Kingdom between October 1925 and December 1995. They were originally set up to spot enemy aircraft. Later, if the Cold War had become a nuclear war, their job would have been to spot nuclear explosions and report their observations back to control centres.
A total of 1,563 underground posts were built and over 10,000 civilian volunteers recruited. If a nuclear bomb had been dropped on Newcastle the nearby ROC posts would have identified the direction, distance and magnitude of the explosion. You might think that a nuclear bomb would be hard to miss but, of course, the government in London could not accurately know what had happened to Newcastle and would have needed accurate reports.
The red symbols on the map below would have been used by the ROC in the advent of war to indicate a ground burst. The green symbols would indicate an air burst. The distinction is important. The fireball of a ground burst touches the ground and earth is sucked up in the mushroom cloud. A lot of radioactive fallout is generated. Fallout is much less of a problem with air bursts. An air burst produces much less fallout than a ground burst because the nuclear fireball does not touch the surface. With ground burst the ROC posts would also report wind direction and force so that fallout patterns could be predicted.
I have a collection of cold war calculators. The ROC shelter ventilation calculator below is the most recent addition to the collection. It allowed the ROC to calculate how much ventilation was needed in a fallout shelter to support a given number of people.
For more posts about Cold War calculators click on the Cold War Calculators category on the right.