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The number of Underground Monitoring Posts (UMPs) constructed in Norfolk amounted to 55, 17 of these sharing their site with an Orlit post. To date, 15 of the sites have been demolished. They reported to a Group HQ in Sprowston, Norwich, which was demolished in 2008. The Norfolk ROC posts formed part of Group 6.

The Royal Observer Corps was a uniformed volunteer organisation, which has enjoyed a long association with the Royal Air Force. The motto of the Royal Observer Corps is: Forewarned is Forearmed, and it would appear that the earliest system for the detection and reporting of aircraft was started late in 1914. Police constables were instructed to telephone reports of any aircraft including Zeppelins, seen or heard within 60 miles of London to the Admiralty, who were in charge of the defences at that time. In 1915, it was decided to extend the area covered by this arrangement, to East Anglia, Northamptonshire, Oxfordshire, Hampshire and the Isle of Wight.

In September 1941, due to the increased call-up of manpower, women were admitted to the Corps. In addition to reporting all aircraft flying over land, or the sea belt adjoining the coastline, ROC personnel on duty by then also assisted aircraft that were lost or in distress. On Saturday 10 May 1941, ROC posts in the Durham, Galashiels and Glasgow Groups were responsible for tracking and reporting what transpired to be the arrival of Rudolph Hess.

High quality Navy binoculars were issued and the observation posts were at first nothing more than a wooden shed located next to a telegraph pole, which connected them to the local telephone exchange. These were eventually replaced by more substantial brick-built structures, protected by sandbags, sited in playing fields, on hilltops or rooftops of public buildings and factories. The posts were manned continuously from 3rd September 1939 to 12th May 1945.

In 1955, the Corps was given the nuclear reporting role by the Home Office and in the early 1960s, Nuclear Reporting Cells (NRCs), were set up at Air Defence Operations Centres and subsequently at other key military establishments in the UK. A series of posts for the observation of aircraft was built for the new organisation. These were substantial structures that offered some level of protection from the elements or attack. Many were made of pre-cast concrete panelled structures known as “Orlit” posts, after Orlit Ltd the manufacturers. These structures were split into two sections: the entrance door led into the smaller roofed section which was used as a shelter and store; a sliding door led to the open section, which housed the post instrument and chart on top of a wooden mounting. There were two varieties: the "Orlit A" was at ground level and the "Orlit B" was raised on four 6ft legs with a ladder for access. Between 1952 and 1955, more than 400 Orlits were constructed.

Between 1958-1968, a countrywide building programme resulted in a network of 1,563 underground monitoring posts, located approximately 8 miles apart and distributed throughout Britain at an estimated cost of almost £5,000 each. The posts were 25ft deep and built of reinforced concrete, waterproofed with bitumen. The whole structure was then covered by a compacted soil mound. Entry was via a steel ladder in a vertical shaft leading to a single room, providing accommodation for three observers to live and work, with a separate compartment with a chemical toilet. Air was circulated from grilled ventilators at both ends of the post and electricity was provided by a 12 volt battery, charged occasionally by an electric generator. Instruments detected the size of any nuclear burst, together with the location and levels of radiation. Conditions were cramped, cold and in some cases damp.

Following the 1990 defence spending review, the ROC post and control personnel were stood down on 30th September 1991. Many of the ROC posts have since been dismantled or sold and sadly, quite a number have been trashed by vandals. For more detailed information go to: Link