The Imperial Japanese Navy in World War II, at the beginning of the Pacific War in December 1941, was the most powerful navy in the world. During the first years of the war the Imperial Japanese Navy dominated the Western Pacific. However, after a series of defeats it lost control of the Western Pacific and collapsed by the end of the war. The naval air service was one of the most potent air forces in the world before its destruction in World War II. Nearly all of its ships were sent to the bottom of the sea by the war's end.