Asdics at war [underwater acoustics]

The U-boat provided the cornerstone of German naval strategy in the two world wars of the 20th century. The author recounts the role of underwater acoustics in defeating this "terrible instrument of war". The author describes the development of underwater acoustic techniques (known as asdics and based on hydrophones and later, acoustic ultrasonic echo-ranging) during the first world war, the inter-war years, and during the second world war. Post war developments are briefly reviewed.