A World War II Deep Shelter and Two Concrete Sound Mirrors uncovered at Fan Hole near St Margaret’s at Cliffe
By Richard Hoskins, Dover Archaeological Group
In 2012 the National Trust, following an appeal, purchased the remaining section of the White Cliffs between Dover and St Margaret’s. The purchase included the site of a system of World War II tunnels known as the Fan Hole Deep Shelter together with two early 20th century concrete sound mirrors - acoustic listening devices that pre-date the invention of radar. The entire complex had been buried in the 1970s as ‘an eyesore’.
The Site
The site is now an important part of UK conflict archaeology and is unique because the two sound mirrors were located alongside the entrances of the deep shelter tunnels. The deep shelter was built in World War II to provide accommodation for the crew of 185 men and 4 officers during hostile bombardments. Its main entrance is at the top of the escarpment, through a steep staircase of 126 concrete steps which lead to the system of tunnels below. The clearance of the rubble infill from the entrance stairway was carried out by members of the Kent Underground Research Group between October and November 2013. This was followed by the repair of unlined ceilings and replacement of the missing wooden structural supports which had rotted after 70 years of exposure to dampness. Distributed throughout the tunnels is a wide range of graffiti, mainly incised into the chalk or written in pencil on the steel tunnel linings. Much of this dates to the period of military occupation although some is the work of more recent intruders (Champion, M.J. 2014).
In May 2014 the Dover Archaeological Group (DAG) was invited to carry out a short excavation in which the precise position of the two sound mirrors was located. Between 6th and 30th October 2014 members of DAG returned to carry out a watching brief during the machine bulk reduction of soil deposits covering the sound mirrors and lower tunnel entrances. With immense skill, the machine operatives removed around 600 tonnes of mixed chalk and soil from the 45 degree slope of Fan Hole and the areas in front of the two sound mirrors. The North Sound Mirror, built in 1917, and one of the earliest in existence, was found to be intact apart from some damage to its northern edge which is believed to have occurred during the digging of the adjacent tunnel entrance in 1940/41. Its smooth concrete surface is slightly ‘crazed’ by a network of narrow cracks although these are also visible on a photograph taken around 1975, shortly before the complex was buried.
The South Sound Mirror is believed to date to the mid 1920s; its shallower dish, which would have had a greater range than the earlier mirror, was also intact although its upper edge had been damaged prior to its burial. A triangular concrete apron on the slope above this mirror, which is believed to have served to prevent water from seeping behind it, was also found in a damaged condition. Although the South Sound Mirror is shallower than its northern companion the dished areas of the two mirrors are similar and both measure around 4.6m (15 feet) in diameter.
By World War II the sound mirrors had become obsolete but were used as convenient locations for the lower entrances to the two tunnels of the newly-built deep shelter. The tunnel entrance beside the South Sound Mirror was opened during the recent excavations but the entrance to the northern tunnel has not yet been completely cleared. A brick-built blast wall, approximately 2.5m high, was built in front of each of the two tunnel entrances and partly.
overlapping the front of the sound mirrors. These were to protect the tunnels from the shockwave of any explosion immediately outside and in front of them. Also in front of each of the sound mirrors is a brick-built latrine block, that at the northern mirror providing facilities for the officers serving inside the deep shelter and the one at the south for the other ranks. The blast walls and latrine blocks at both locations were uncovered during the excavation and although damaged were found to be in adequate condition for conservation.
The National Trust plans to open the complex to guided, torch-lit tours in May 2015 and is looking for around 70 volunteer tour guides to help in this.
If any KAS members are interested in helping please call Jon Barker at the National Trust on 01304 200004 or email Jon.Barker@nationaltrust.org.uk