By the time Raeder met with Hitler for a detailed discussion of naval strategy in April 1942, the usefulness of aircraft carriers in modern naval warfare had been amply demonstrated. British carriers had crippled the Italian fleet at Taranto in November 1940, critically damaged the in May 1941 and prevented the battleship from attacking two convoys bound for Russia in March 1942. In addition, a Japanese carrier raid on Pearl Harbor had devastated the American battle fleet in December 1941. Raeder, anxious to secure air protection for the "Kriegsmarine"s heavier surface units, informed Hitler that "Graf Zeppelin" could be finished in about a year, with another six months required for sea trials and flight training. On 13 May 1942, with Hitler's authorization, the German Naval Supreme Command ordered work resumed on the carrier.