A relic from Sheppey’s wartime past is slowly being washed away.

The acoustic mirror, located just along the beach at Warden Bay, is believed to date back to the 1920s, and was used as an early detection system for enemy aircraft.

The installation pre-dates the widespread use of radar technology in the military, and its concave shape was designed to gather and amplify the sound waves generated by oncoming enemy planes.

The large stone structure is now split in half and big chunks are lying around its base, being lapped by the waves.

Peter West, research historian at Blue Town Heritage Centre, said there were lots of sound mirrors around the coast.

“They were usually built in threes, and you would have a guy sitting in front of it with a set of earphones and another as far down the coast as possible, but still in range of radio communication, and they would triangulate the sound" - Peter West

Others were placed at Abbot’s Cliff, Denge, Dover, Hythe and Joss Gap.

Mr West said: “They were usually built in threes, and you would have a guy sitting in front of it with a set of earphones and another as far down the coast as possible, but still in range of radio communication, and they would triangulate the sound [to determine the position of enemy aircraft].”

He said the Warden Bay acoustic mirror would have been on top of the cliff to give as wide a spread as possible, but it has slipped down on to the beach as the cliff has collapsed over the years due to coastal erosion.

It is included on a map at Blue Town Heritage Centre, as part of its Barbed Wire Island project.

Laurie Harpum is one of four artists invited by the Kent Artists Network to put on an exhibition at the Royal Engineers Museum at Brompton based on its collection.

She has been looking at the acoustic mirror as well as an old pillbox she used to play in as a child in Eastchurch, as part of the project.

The organiser of last year’s Love Sheppey X festival said she was drawn to the mirror’s striking appearance.

She said: “Sheppey’s history is really hidden. In other areas where they have these sound mirrors they are still up on the cliffs whereas ours has kind of fallen into the cliff. It feels like we should be doing something to look after it. It’s beautiful.”

Ms Harpum’s display, titled Artefacts, will run from March 17 until April 12.