Operational instruments of the Royal Observer Corps
The Royal Observer Corps (ROC) was a civil defence organisation operating in the United Kingdom between October 1925 and 31 December 1995, when the Corps' civilian volunteers were stood down. (ROC headquarters staff at RAF Bentley Priory stood down on 31 March 1996).
Source: Wikipedia — Operational instruments of the Royal Observer Corps (CC BY-SA 4.0)