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.
At one time, these tiny bunkers were dotted in a grid pattern across the landscape of the UK: by 1968, more than 1,500 had been constructed. However, many have now been lost – ploughed back into the land by the farmers on whose land they were built. (Others, like those at Portadown and Skelmorlie, have been restored and you can visit them for yourself on open days.)