Why British cruisers carried ASDIC

British cruisers of the 1920s and 1930s carried ASDIC or hydrophones even though submarine hunting was not their main role. The fitting is traced to the shock of losing Aboukir, Cressy, and Hogue to one submarine during the First World War. That memory kept anti-submarine protection unusually prominent in British warship requirements and persisted as normal practice long after the disaster. Sonar affected hull form, electrical demand, systems, and crewing, though these installation demands were manageable. The associated operating habits also affected controls and training. Constant zigzagging added another operational cost by slowing formations and requiring crews and steering systems prepared for repeated course changes.