Why Was the Matsushiro Underground Complex Built?
Plans to Move Japan’s National Center Inland
Before the Pacific War, the Japanese Army regarded Tokyo as vulnerable because of its proximity to the coast and its location on the edge of the vast Kanto Plain. The situation became far more serious in July 1944, when Saipan fell to Allied forces. Air raids on the Japanese mainland and the possibility of an invasion became increasingly realistic, prompting Japanese military and government leaders to consider moving key national functions away from Tokyo.
In July 1944, during the final Cabinet meeting of the Tojo administration, a plan to relocate the Imperial Palace, Imperial General Headquarters, and major government functions to Matsushiro in Nagano Prefecture was formally approved.
This decision marked the beginning of the enormous underground construction project that became known as the Matsushiro Underground Imperial Headquarters.
Why Was Matsushiro Chosen?
A Strategic Inland Location
Matsushiro was selected for a combination of geographical, geological, logistical, and symbolic reasons.
The area lies deep inland on Honshu and was considered less vulnerable to air attack than Tokyo. It is surrounded by mountains and has extensive areas of solid bedrock, making it suitable for constructing large underground facilities.
The nearby Nagano Airfield was also considered advantageous for transportation and communications. In addition, the surrounding rural communities were thought to provide a large labor force while making it easier to maintain secrecy.
Conditions Considered Suitable for the Project
The planners considered Matsushiro attractive because of its stable inland location, the hardness of its bedrock, the availability of a broad plain surrounded by mountains, and the amount of land available for large-scale construction.
The site was also believed to offer geological strength capable of withstanding extremely powerful bombs. In addition to these practical considerations, symbolic associations were reportedly attached to the names Shinshu and Matsushiro, further reinforcing the area’s perceived suitability.
The Three Underground Complexes
Zozan Underground Tunnels
The Zozan Underground Tunnels form part of the approximately 10-kilometer network constructed beneath the Matsushiro mountains. Government offices, communication facilities, the Japan Broadcasting Corporation, and the Central Telephone Office were planned for this section.
The first major blasting operation took place at 11:11 a.m. on November 11, 1944, marking the beginning of full-scale construction.
The tunnels were excavated using rock drills, explosives, carts, and large amounts of manual labor. Evidence of the construction methods can still be seen inside the tunnels today.
A complicated network of passages was created, with rooms intended for offices, communications, and other essential functions. A section has been reinforced and maintained as a visitor route, allowing people to walk through the actual wartime tunnels.
Maizuru Underground Complex
The Maizuru Underground Complex was planned as the central area for the Imperial Palace and Imperial General Headquarters. Reinforced-concrete buildings were constructed above ground, including facilities intended for the Emperor, Empress, and the Ministry of the Imperial Household.
The buildings were carefully designed to blend into the mountain landscape and reduce the possibility of detection from the air. Some of these structures have survived and are open to visitors.
Minakami Underground Complex
The Minakami Underground Complex was initially considered as a possible location for the Imperial Palace and Imperial General Headquarters. However, concerns about the stability of the ground led to changes in the plan.
The site was eventually intended primarily for the storage of supplies. Together, the three underground complexes formed an enormous system supporting a national-scale relocation plan that would have effectively transformed Matsushiro into Japan’s wartime center.
Plans to Relocate the Imperial Palace
From Mount Minakami to Mount Maizuru
The original plan called for the Imperial Palace to be established beneath Mount Minakami. When the geological conditions there were found to be unsuitable, the plan was changed and Mount Maizuru became the preferred location.
Facilities for the Emperor and Empress, as well as buildings associated with the Imperial Household Ministry, were planned at Maizuru. Their design was intended to make the complex difficult to detect from the air.
Other supporting facilities were also planned throughout the Nagano Basin, including communication transmission facilities, accommodation for members of the imperial family, and an expanded Nagano Airfield.
The scale of the project was so immense that it amounted to a plan for a wartime relocation of Japan’s national center.
A Massive Construction Project Kept Secret
The Secret “Matsushiro Warehouse Construction”
Construction was officially carried out under the deliberately vague name “Matsushiro Warehouse Construction”. Despite efforts to maintain secrecy, the enormous scale of the work gradually led to rumors among local residents that the Emperor and Imperial General Headquarters would be moved to Matsushiro.
Large quantities of construction materials were transported by railway, making the project increasingly difficult to conceal.
Workers and Harsh Conditions
Both Japanese workers and many Korean laborers mobilized from the Korean Peninsula were involved in the construction. At its peak, approximately 10,000 people are said to have worked at the site.
Construction continued around the clock under extremely difficult conditions. Explosives were used to blast through the rock, while excavated material was carried away largely by manual labor. The dangerous working environment resulted in many victims, and the history of the site also reflects the suffering experienced by workers during wartime.
A Plan Abandoned Before Completion
The End of the War
The Matsushiro project was approximately 75 percent complete when construction was halted following Japan’s acceptance of the Potsdam Declaration on August 15, 1945.
The Emperor ultimately remained in Tokyo rather than relocating to Matsushiro. The planned wartime relocation was therefore never carried out.
However, records and diaries indicate that officials connected with the Imperial Household Ministry inspected Matsushiro shortly before the end of the war. These records show that the possibility of relocation was being seriously considered as the situation deteriorated.
Although the plan was never completed, the Matsushiro underground complex stands as a reminder of the increasingly desperate circumstances facing Japan during the final stage of the war.
What Happened After the War?
From Wartime Facility to Place of Historical Preservation
After the war, some of the buildings at Mount Maizuru were used as facilities for war orphans before later being converted for use by the Matsushiro Seismological Observatory of the Japan Meteorological Agency.
The area eventually became an important center for earthquake observation. Seismological instruments were installed in the underground facilities, giving part of the former wartime complex a completely different role in the postwar period.
In 1990, following efforts by local high school students, part of the Zozan Underground Tunnels was opened to the public.
A memorial to the Korean workers who died during the construction is also located within the site, helping visitors understand not only the military history of the complex but also the human suffering associated with its construction.
Walking Through the Zozan Underground Tunnels
Experience the Scale of the Wartime Construction
Today, visitors can enter a section of the Zozan Underground Tunnels and walk through the passages that were excavated during the war.
Marks left by rock drilling and traces associated with the tracks used to move excavated material provide tangible evidence of the enormous effort required to create the underground network.
Inside the tunnels, the atmosphere is quiet and subdued. The rough rock walls and narrow passages make it easier to imagine the scale and difficulty of the construction work carried out under wartime conditions.
A Place for Peace and Historical Education
The Matsushiro Underground Imperial Headquarters Ruins are not simply military remains. They are also an important place for peace education and learning about modern Japanese history.
Schools, groups, and individual visitors come to the site to learn about the final stages of World War II, the realities of wartime mobilization, and the human cost of large-scale military construction.
Interpretive signs and information panels help explain the history of the tunnels and the people involved in their construction.
Visitor Experience and Access
Visiting the Zozan Underground Tunnels
A section of the Zozan Underground Tunnels has been made safe for public visitation. Guided tours with explanations by staff are also available, with advance reservations required for some programs.
The underground environment remains relatively cool even during the warmer months, making the tunnels an interesting place to visit throughout the year.
Getting There
From Nagano Station, Matsushiro can be reached by bus in approximately 30 minutes. The site is also within walking distance of the former Matsushiro Station area, making it convenient to combine with other attractions in the historic district.
Parking is available, making the site accessible by car as well.
What to Wear
The tunnels are dark in places, and some surfaces can be slippery. Comfortable walking shoes and a light jacket are recommended.
Some sections also include narrow passages and steps. Visitors who have concerns about mobility or physical stamina should check the conditions of the visitor route before entering.
Explore the History of Matsushiro
The Matsushiro Underground Imperial Headquarters Ruins can be combined with the area’s many other historic attractions, including Matsushiro Castle, the Former Sanada Residence, the Sanada Treasures Museum, and Bunbu School.
Exploring these sites together reveals the remarkable layers of Matsushiro’s history, from the age of samurai and the Sanada family to Japan’s modern transformation and the events of World War II.
A Place to Remember and Reflect
The Matsushiro Underground Imperial Headquarters Ruins are among the most significant wartime remains in Nagano Prefecture. The tunnels preserve the physical traces of an enormous project undertaken during one of the most difficult periods in modern Japanese history.
Walking through the underground passages offers more than an encounter with an unusual historical site. It provides an opportunity to consider the realities of war, the experiences of the people who built the tunnels, and the consequences of decisions made during a time of national crisis.
For travelers interested in Japanese history, modern Japan, military history, or peace education, a visit to the Zozan Underground Tunnels provides a deeply meaningful experience and an important connection to the past.