If German forces were successful in invading Britain during the Second World War, the dozens of Zero stations would have come into operation. They were designed so that spies could secretly give information to out stations, before the coded information was passed on via radio to zero stations who would then inform the Special Duties HQ at Wiltshire by a direct line.
Both men and women were chosen to work as part of the Special Duties Organisation, usually people in jobs which involved travelling such as doctors, farmers and postmen, to avoid suspicion. If an invasion happened, they would continue in their job yet be able to still pass on messages to a radio operator. It sounds like something out of a film yet was designed to save Britain. Secret messages were left in disguised letter boxes such as holes under rocks or in trees.
A control station was operated by three women where two transmitters and two receivers were kept; one for training and one for real. Whilst the training set was often kept in a building above ground, the real kit was kept underground at ‘Zero Stations’.
Accessed via a hatch and ladder, like an ROC post, underground the first resembled an air raid shelter with a corrugated roof and this hid the access to the following room to make it look like a storage bunker. Hidden behind what would have been shelves and boxes was the entrance to the next room where the radio equipment would have been. A 16ft tunnel leads to the emergency exit.
A couple of clever disguises still remain. The tree trunk by the entrance is original and had a groove cut into it to hide an aerial wire, which would have had bark covered over it.