Advances in convoy tactics, high frequency direction finding (referred to as "Huff-Duff"), radar, active sonar (called ASDIC in Britain), depth charges, ASW spigot mortars (also known as "hedgehog"), the intermittent cracking of the German Naval Enigma code, the introduction of the Leigh Light, the range of escort aircraft (especially with the use of escort carriers), and the full entry of the U.S. into the war with its enormous shipbuilding capacity, all turned the tide against the U-boats.