The sea has eaten away 100 yards or more of land in the past 50 years and concrete tank blocks, once at the base of the cliff, now lie where they are covered at high tide.
Many more of the country's wartime relics are disappearing and there is no full record of those that remain. So now members of the Fortress Study Group are setting out to make a complete record of every old pillbox, tank block and gun battery in Britain.
Sam Watson, 36, is a postman at Withernsea, but his real enthusiasm is concrete. Whenever he has any spare time he is down on the beach exploring what remains of Godwin battery and other fortifications designed to keep the German fleet from invading the Humber. Last week, on the beach near Kilnsea, he examined two huge pieces of concrete about 7ft thick and more than 20ft across.
'These two pieces fell off the cliff last year. They are part of the foundation for a 9in naval gun,' Mr Watson said. 'The pieces are upside down now but you can see a ring where the gun was secured and the track on which it ran can be seen in the cliff.'
There used to be a line of pillboxes connected by a tunnel to the military camp behind. Now all that remains is a jumbled reef of concrete covered in bright green seaweed and a few pieces of steel girder which are uncovered at low tide.
The Fortress Study Group has documented 400 sites in the Holderness area north of Hull and is hoping bit by bit to cover the whole country.
It wants good examples of Second World War fortifications to be preserved as part of our national heritage. But just two weeks ago Ravelin battery at Sheerness in Kent, originally equipped with two 9in guns, was demolished in order to build a Tesco supermarket. As it was not listed as a national monument it could not be protected.
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