On December 7, 1941, the Japanese launched a surprise attack on Pearl Harbor. Within a short time, five of eight U.S. battleships were sunk or sinking, with the rest damaged. All three American aircraft carriers were out to sea, however, and evaded destruction. The sinking of the British battleship and battlecruiser , demonstrated the vulnerability of a battleship to air attack while at sea without sufficient air cover, settling the argument begun by Mitchell in 1921. Both warships were under way and en route to attack the Japanese amphibious force that had invaded Malaya when they were caught by Japanese land-based bombers and torpedo bombers on December 10, 1941.