The U.S. military had plans to launch nuclear attacks from Japan's main islands in the 1960s in the event of a crisis in the region, according to State Department documents.
The secret communications, declassified in July 1998, indicated U.S. forces were prepared to transport nuclear weapons deployed on Okinawa, which was under U.S. rule, to military bases in Japan for possible attacks on China or the Soviet Union.
Okinawa was ruled by the United States from the end of World War II until 1972.
Due to Japanese government opposition to the proposed storage of nuclear weapons in Japan, the U.S. military had considered ways to carry the weapons to the main islands in the event of an emergency, according to one item of correspondence.