On 15 June 1944 American forces invaded the island of Saipan thus piercing the first hole in the inner line of island fortifications that the Japanese had laboriously constructed in order to defend their homeland, their empire, and their recent conquests in the western Pacific and in Asia. Saipan is 1,270 nautical miles from Tokyo, 1,430 from Manila, 1,640 from Shanghai, and 3,350 from Honolulu. Located in the southern portion of the Marianas chain, it was the most heavily fortified of that group of islands and was considered by the Japanese to be a keystone in the defensive system for the homeland.