Used in anti-Submarine operations in conjuction with the ASDIC ( Allied Submarine Detection Investigation Committee) equipment and measured the range of an enemy submarine with ultrasonic echo on board equipment.
Dial marked in yards and seconds and measured the speed of sound in seawater in seconds.
Front face marked 'Admiralty Pattern No 6 Swiss Made'.Back case opens to reveal working mechanisms.Cover stamped 250185 and 64407 on mechanism face. Rear of watch on case cover is etched owner details 'Ronald Alan Lyddon 31885, 21 Yung. This is an address in Singapore.Britain had a very large Naval base and thousands of R.N. Servicemen were stationed in Singapore. In Full working order