Information from Wikipedia.
The Royal Observer Core (ROC) provided an additional and highly useful function to the war-time UK Government by providing a plausible cover story for a number of covert war-time operations. Up to twenty highly secret electronic warfare units were established across the UK, with their associated scientists and technicians being dressed in ROC uniforms so as to avoid arousing any suspicion while entering and leaving RAF, Army and Royal Navy establishments.
Throughout the Second World War, ROC personnel were paid expenses and allowances in cash via their Group HQ and several Deputy Group Commandants discovered that they had up to one hundred additional observers appearing on their staff role, each receiving higher than normal allowances, despite these individuals having never reported for duty.
A notable example of one such cover story involving the ROC is that which took place at RAF Little Rissington, where a series of tunnels were excavated during the 1940s. RAF Little Rissington forces personnel and local residents were informed that this activity was associated with an ROC unit, which was indeed seen to be manned by individuals wearing ROC uniforms. The ROC however had no knowledge of the existence of this supposed ROC facility until many years after the war. The true nature of the activities of these Ghost ROC personnel remains classified information, with public access to related documents being denied until 2045.