During the first six months of the war Japanese naval air power achieved spectacular success and spearheaded offensive operations against Allied forces. On 7 December 1941, the IJN's "Kido Butai" attacked Pearl Harbor, crippling the U.S Pacific Fleet by destroying over 188 aircraft at the cost of 29 aircraft. On 10 December, Japanese naval land based bombers operating from bases in Indochina, were also responsible for the sinkings of HMS "Prince of Wales" and HMS "Repulse" which was the first time that capital ships were sunk by aerial attack while underway. In April 1942, the Indian Ocean raid drove the Royal Navy from South East Asia. There were also air raids carried out on the Philippines and Darwin in northern Australia.