Science: Calling All Fish

Up the west coast of England last week crept the French Navy's minesweeper Siam, spying on schools of herring. Its assignment : to learn how to hunt fish with ASDIC (developed for the Allied Submarine Device Investigation Committee, from whose initials it took its name).

ASDIC, designed for submarine hunting, sends ultrashort sound waves through the water and any sizable object reflects them. During the war, this fact frequently caused depth-bombing of whales, torpedoing of schools of pilchards. But as ASDIC and its operators improved, they learned to distinguish skillfully between echo-making objects,...