There is a mention of sound mirrors in the article Mirrors and smoke: A. V. Hill, his Brigands, and the science of anti-aircraft gunnery in World War I, William Van der Kloot. DOI: 10.1098/rsnr.2010.0090 Published 20 July 2011.
Acoustic early warning systems, spectacular remnants of a dead-end technology on the British coast
There is a mention of sound mirrors in the article Mirrors and smoke: A. V. Hill, his Brigands, and the science of anti-aircraft gunnery in World War I, William Van der Kloot. DOI: 10.1098/rsnr.2010.0090 Published 20 July 2011.