This concrete installation on the edge of Fulwell Allotments is one of only a few left in the whole country.

This is an acoustic mirror, built in 1917 to detect sound from German zeppelins sent to the region to bomb ports and shipyards. It is 4m here, and acts as an early warning system a decade and a half before radar was fully implemented. Action was needed after a zeppelin raid over the Wheatsheaf area of Sunderland in April 1916 left 22 people dead and 100 injured.

Though many survived, it left unrelenting trauma. A lady named Mary Boster of 6 Milburn Terrace lived with epileptic fits since the age of nine, and increased in frequency since the raids. The shock of the raid at such a young age impacted her for the rest of her life. It was her and others experiences which required this installation.

There’d be a fella stationed in a bunker listening in with a microphone stuck on the plinth in front. He’d be able to give a 15 minute warning to the city to evacuate and prepare for an oncoming attack. Those manning it would be highly experienced after using detection methods taught in the trenches. The method would include using a stethoscope headset connected to a microphone above his head which would retrieve the optimum sound. Combined with the doppler effect, it would track the course and direction of the enemy.

He would signal the alarm to his superiors to enable to whole population to seek shelter and sanctuary.

The mirror was in a ruinous state for decades up to 2015, but was restored by Historic England, Sunderland City Council and the Heritage Lottery Fund in partnership with Limestone Landscapes in 2015. This has meant this incredible wartime relic can continue to inspire.