The Imperial Japanese Navy in World War II, at the beginning of the Pacific War in December 1941, was the third most powerful navy in the world, and the naval air service was one of the most potent air forces in the world. During the first six months of the war, the Imperial Japanese Navy enjoyed spectacular success inflicting heavy defeats on Allied forces, being undefeated in every battle. The attack on Pearl Harbor crippled the battleships of the US Pacific Fleet, while Allied navies were devastated during Japan's conquest of Southeast Asia. Japanese naval aircraft 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. After these successes, the Japanese now concentrated on the elimination and neutralization of strategic points from where the Allies could launch counteroffensives against Japan's conquests. However, at Coral Sea the Japanese were forced to abandon their attempts to isolate Australia while the defeat at Midway saw them forced on the defensive. The campaign in the Solomon Islands, in which the Japanese lost the war of attrition, was the most decisive; they had failed to commit enough forces in sufficient time.