ASDIC used an active sound transmitter and receiver with a steerable head, producing bearing and range rather than depth. A water-filled metal dome helped isolate the set from flow noise at moderate speed. Above about eighteen knots, self-noise impaired contacts, so a fast fleet might have to rely on speed and zigzagging rather than useful sonar search. Rough conditions, fish, whales, wakes, currents, and thermal layers could all confuse the picture. Skilled operators and a realistic understanding of these limits mattered as much as the hardware.
Chapter · 1:17:30-1:23:16
ASDIC found range and bearing, not certainty
ASDIC gave escorts a directional echo and range, but speed, weather, thermal layers, and false contacts limited its use.