If you have even a passing interest in civil defence and preparations for nuclear attack on the UK, you’ll quickly come across ROC posts.
These are small, three-person bunkers, built by the government in the 1950s, and formerly manned by members of the Royal Observer Corps (ROC).
Known as ‘observers’, the mission of these civilian volunteers was to go to their monitoring post when nuclear attack was imminent, and detect and report the direction and power of any bomb blasts. Readings from several posts could be taken together to triangulate the precise location where a nuclear weapon had hit.