Heritage Hotspots - Acoustic Mirror The south east of England is well-known for its First- and Second World War anti-aircraft defences, whether they be radar or other anti-air installations, gun entrenchments or sea defences. The east coast of England and Scotland was also a place for these defences, as they were the nearest coast to the Baltic States and Germany from which air raids originated. Teesside is included in this defensive perimeter set up by the wartime governments, and we have an acoustic mirror situated in the heart of one of our towns, Redcar. The mirror, now set in an unassuming residential area south of the town centre, was a vital component in protecting Britain during the latter stages of the First World War. The technology behind the listening device is thought to have been developed in the early years of the 20th century, as aircraft developed and were increasingly used in warfare. The devices varied from mirrors, discs and bowls. The mirror in Redcar is concave, with two flanking walls. This shape helped to ‘catch’ the sound and the walls were an attempt to deflect interference. Interference was a problem for these early warning devices, as adverse weather – which locals will tell you is frequent! - could hinder any listener. The listener would have headphones connected to a microphone set on a small metal post in front of the mirror. The Redcar mirror formed part of a chain along the north east coast, along with one in Boulby, Sunderland and Humberside. As aircraft technology adapted and improved, these listening posts become more and more redundant. This was mainly because of the speeds that aircraft could now reach, which left little to no time for a listener to sound any warning. This led to the introduction of radar, which was a much faster of detecting and warning of incoming aircraft. The mirrors were used as a backup, should the radar systems be a victim of jamming, but they were increasingly left and now stand as a memorial to the efforts undertaken to protect Britain against attack in the biggest wars of the 20th century. Sunderland's mirror with the microphone post. c.BBC Like many wartime defences, we sometimes forget they are there, or walk past them without noticing them. However, they all formed part of the defence of Britain and helped us to keep our shores free from invasion and, London aside, free from catastrophic damage. They did not always prevent attacks, as attacks on Hartlepool and Scarborough (and others) showed, but perhaps they stopped many more. Next time you see a memorial or remnant of either war, perhaps stop and contemplate just how much the humble structures helped to protect the landscape around them.