The 1930s were the last time that the Japanese military focused on production and design of tanks before World War II. After that period, they were largely preoccupied with establishing naval control and their focus was on production of ships and aircraft. Furthermore, with the emphasis on expansion southward into the Pacific Ocean region, land battles would be largely replaced by naval warfare, and thus, with the exception of small islands, the domain of the Imperial Japanese Navy. With the destruction of the Imperial Navy, the focus on tanks returned when the Japanese military prepared for the defense of the mainland in the last years of World War II.