Secret War Tunnels Revealed Near Tokyo

Allied Air Raids Prompt a Clandestine Munitions Factory

During my recent trek out to Saitama to explore The Hundred Caves of Yoshimi, I discovered the subterranean world lurking beneath the caves kept a secret military installation. Juxtaposed with the timeless burial tombs above is a netherworld carved out of military ambition. It’s relatively secluded location in rural Saitama, some 50 km from Tokyo proper offered some hope that it would remain hidden from allied radar.

In 1945 during the closing stages of the Second World War attempts were made to establish a clandestine Nakajima Aircraft Company facility to manufacture munitions owing to air strikes by American B-29 bombers at its then Omiya facility. From mid-1944 and increasingly until the end of the war Japan was subject to strategic air raids targeted at industrial facilities and munition depots.

Excavation of the tunnel system which included three main tunnels running deep into the sandstone hills required the concerted efforts of between 3,000 and 3,500 Korean labourers requisitioned from coal mines, factories and railway construction sites across the country. Further testament to the strategic importance of the tunnels was a paid visit by then Prime Minister Kantaro Suzuki in July 1945 to oversee its progress.

Working in companies of 500, the Korean labourers undertook the dangerous task of soil and stone removal from the four metre wide tunnels after blasting along with arduous pickaxe digging. From the start of 1945 until the September when Japan surrendered, a total 6.7 km of tunnels had been dug in a grid like pattern, equating to roughly 80 percent of the planned complex. Interestingly after the war much of the tunnelling equipment including Swiss and American made machine tools were seized by US military command and transferred to the Chiang Kai-shek regime as restitution.

Needless to say this monumental engineering feat never saw the light of day so to speak with the factory not realising production. Confirmation of this expansive tunnel network is still evident with many tunnel passages gated up with only about ten percent open to the public. Walking through the tunnels certainly has an eerie quality and peeking into the dark recesses through the gated up divides provides a fleeting glimpse into their vastness.

Yoshimi War Tunnels Quick Facts:

Official name: Second munitions arsenal No.855

Construction: September 1944 to September 1945

Estimated cost: 40 million yen (1945)

Workers: 3,000 ~ 3,500

Tunnel length: 8.4 km dug in a grid pattern (6.7 km completed)

Tunnel height: 2 ~ 4 metres

Tunnel width: 4 metres

Total area: 10,000 square metres (8,000 Sq m completed)