Homeland Defence

This theme covers the defences Japan built against invasion and air attack: the coastal fortresses and batteries of the Meiji era onward, anti-aircraft gun positions and observation posts, and the underground headquarters, aircraft shelters and coastal positions dug in 1944–45 for the "decisive battle on the home islands".

Modern home defence began with the shogunate's shore batteries. From 1880 the Meiji government built Western-style batteries at the mouth of Tokyo Bay, followed by fortresses at Yura (the Kitan Strait), Shimonoseki, Geiyo, Hiroshima Bay, Sasebo, Nagasaki, Maizuru, Hakodate, Tsushima and elsewhere, with heavy guns in brick, stone and concrete emplacements and strict controls on surveying and photography under the Fortified Zone Law. From the 1920s some fortresses were wound down after naval disarmament while others received turrets from scrapped warships. Late in the Pacific War the threat became air raids and invasion. After the fall of Saipan in July 1944 the Army began preparing for ground combat at home and started a vast tunnel complex at Matsushiro in Nagano to house Imperial General Headquarters and the government. In spring 1945 it drew up Operation Ketsu-Go, the planned defence of the home islands, which expected landings in southern Kyushu and the Kantō: newly raised divisions and cave positions were placed around Shibushi Bay, the Miyazaki coast, Fukiagehama, Kujūkuri and Sagami Bay, and air, surface and underwater special attack forces were massed. The Volunteer Military Service Law of June 1945 made men aged 15 to 60 and women aged 17 to 40 liable for the People's Volunteer Combat Corps. The United States for its part planned Operation Downfall, with landings in Kyushu in November 1945 and in the Kantō the following spring. Japan surrendered in August and the decisive battle never took place.

From the Meiji-era coastal fortresses to the underground headquarters and aircraft shelters dug in 1944–45, Japan built layers of defences against invasion and air attack. The theme shows how Japan's leaders judged the war in its last months and what that cost: the new divisions lacked weapons and training, and building positions and tunnels mobilised great numbers of soldiers, students, residents and Korean labourers, with deaths and injuries among the workforce at Matsushiro and elsewhere. The experience of Okinawa indicates what civilians would have faced had the plan been carried out. From Meiji brick batteries to unlined Shōwa tunnels, the remains also document the evolution of Japanese military engineering.

Under this theme visitors will find fortress batteries, magazines and observation posts; sea forts and turret batteries; anti-aircraft gun pits; concrete aircraft shelters scattered around former airfields; tunnels of underground headquarters and factories; and coastal machine-gun positions and storage tunnels for suicide boats. Some tunnels are closed because of the risk of collapse or can be entered only on guided visits.