The Fan Bay, or Fan Hole, battery was established on the clifftop above Fan Hole, to the north of Dover, in late 1940. It was one of three batteries built to target more effectively enemy shipping in the English Channel, which earlier guns, Winnie and Pooh, set further back from the cliffs, had been very ineffective at to the chagrin of Prime Minister Winston Churchill. Fan Bay’s battery had three naval BL (breech loading) 6 inch Mk VII guns with a range of 14 miles, and was manned by the four officers and 185 men of the 540th Coast Regiment.
To provide shelter for the battery’s gunners, a deep shelter was excavated in the chalk by the Royal Engineers' 172nd Tunnelling Company between November 1940 and February 1941. This followed a familiar construction pattern to other Dover gun battery shelters, with concrete staircases leading deep down below the headland surface to a bomb-proof irregular grid of tunnels formed by a vaulted lining of corrugated steel supported by colliery-type hoops. Mechanical ventilation was provided by galvanised steel overhead ducts, mesh wrapped to take a coating of now missing insulation material.
Fan Bay’s shelter was deeper than others, requiring three flights of stairs to reach its five large underground chambers at 23m below the surface. These would have been used primarily for operational and sleeping accommodation, with sanitary and first aid facilities in addition, and while these were common to all of the Dover batteries, Fan Bay’s additionally had two tunnels running out to the cliff face where two sound mirrors were sited.
The sound mirrors take the history of the site back to near the end of the First World War as the smaller of the two, at 15 ft (4.6m) diameter, dates from c.1917, while the larger 20ft (6.1m) diameter sound mirror was built in the 1920s. Sound mirrors were built on English Channel facing coasts from 1916 onwards to warn of the approach of enemy aircraft, and worked by concentrating sound waves at a central point from which a receiver could channel sound to a trained operator. A section of the tunnels near the original mirror appears to have been constructed in a different manner to the rest of the shelter and may also date from the end of the First World War.
Further information on sound mirrors is available at Sound Mirrors.
The site may have had an earlier naval connection as carved stone posts with a 1909 date and the Admiralty anchor were present on site in recent years.
The tunnels were abandoned after the war and the entrances were covered over and all surface buildings demolished in the 1970s as part of the infamous Operation Eyesore project. Only restricted access has been feasible in recent years