In December 1941, the fleet consisted of nine battleships, three aircraft carriers, 12 heavy cruisers, eight light cruisers, 50 destroyers, 33 submarines, and 100 patrol bombers. This was approximately the fleet's strength at the time of the Japanese attack on Pearl Harbor. That day, the Japanese Combined Fleet carried out the attack on Pearl Harbor, drawing the United States into World War II in the Pacific. The Pacific Fleet's Battle Line took the brunt of the attack, with two battleships destroyed, two salvageable but requiring lengthy reconstruction, and four more lightly to moderately damaged, forcing the U.S. Navy to rely primarily on aircraft carriers and submarines for many months afterward.