 ASDIC (also known as SONAR) was a central feature of the Battle of the Atlantic.One crucial development was the integration of ASDIC with a plotting table and weapons (depth charges and later Hedgehog) to make an anti-submarine warfare system.ASDIC produced an accurate range and bearing to the target, but could be fooled by thermoclines, currents or eddies, and schools of fish, so it needed experienced operators to be effective.