In the 1920s and 1930s the battleship was the ultimate power in naval warfare. But the Japanese, by their attack on Pearl Harbor on 7 December 1941 proved aircraft carriers were now the most powerful weapon. This meant battleships were already out of date. When the war started, Yamato was the flagship of the Combined Fleet commander Isoroku Yamamoto. It spent much of 1942 defending Japanese shipping out of Truk. Torpedoed by a US submarine in 1943 it was under repair until 1944. Because attack from the air was now the main threat, Yamato was fitted with additional anti-aircraft guns. In June 1944 Yamato took part in the Battle of the Philippine Sea. In October Yamato was in the Battle of Leyte Gulf. During the battle she fired her guns at US escort carriers thinking they were full sized carriers. She was attacked by several US destroyers and received some damage. Returning to Japan in November she was again fitted with more anti-aircraft guns. By then Japan no longer had the resources to keep Yamato operating. In 1945, Yamato left for Okinawa as part of the suicidal Operation Ten-Go. It was an effort to attack US ships supporting the Battle of Okinawa. But, off the coast of Kagoshima, it was sunk by U.S. aircraft on 7 April.