Japan has avoided extending its territorial waters to cover five key straits to avoid political disputes arising from the passage of U.S. warships carrying nuclear weapons, according to accounts of former top Japanese officials.

When the boundaries were set in the late 1970s, it was believed the U.S. would have continued to transport nuclear weapons through the channels regardless of whether they were considered Japanese territorial waters or not.

Japan's territorial waters in the Soya, Tsugaru, Osumi, Tsushima and Korea straits have been set at 3 nautical miles (5.6 km) from shore, instead of the maximum allowable limit of 12 nautical miles (22 km).