<P> A set of caves were excavated near Nagano on Honshu, the largest of the Japanese islands . In the event of invasion, these caves, the Matsushiro Underground Imperial Headquarters, were to be used by the Army to direct the war and to house the Emperor and his family . </P> <P> Japanese policy - making centered on the Supreme Council for the Direction of the War (created in 1944 by earlier Prime Minister Kuniaki Koiso), the so - called "Big Six"--the Prime Minister, Minister of Foreign Affairs, Minister of the Army, Minister of the Navy, Chief of the Army General Staff, and Chief of the Navy General Staff . At the formation of the Suzuki government in April 1945, the council's membership consisted of: </P> <Ul> <Li> Prime Minister: Admiral Kantarō Suzuki </Li> <Li> Minister of Foreign Affairs: Shigenori Tōgō </Li> <Li> Minister of the Army: General Korechika Anami </Li> <Li> Minister of the Navy: Admiral Mitsumasa Yonai </Li> <Li> Chief of the Army General Staff: General Yoshijirō Umezu </Li> <Li> Chief of the Navy General Staff: Admiral Koshirō Oikawa (later replaced by Admiral Soemu Toyoda) </Li> </Ul> <Li> Prime Minister: Admiral Kantarō Suzuki </Li>

Which of the following events forced the surrender of japan