A military aircraft hangar built during the war to protect military aircraft from enemy planes. From the outside it looks well preserved, but apparently its rebar was taken during the Korean War, so the inside is in shaky condition. What was housed here was the former Imperial Army's Type 3 fighter "Hien." At Osawa No. 1 there was a 1/10-scale statue of the Hien.

A former Imperial Army aircraft bunker (entaigo) at the Mitaka end of Chofu Airfield. Entaigo were built to protect aircraft from enemy air raids. Here's how they were made. First, earth was piled up on the ground into a small hill, sized to fit the aircraft to be housed. Sheets of paper or similar were laid over it and covered with concrete. Some parts were reinforced with rebar, and support pillars were inserted. Once the concrete dried, the soil inside was dug out, and it was complete. Because it's semi-underground and water collects easily, drainage channels were dug inside or drainage pumps installed. Aircraft were backed down a slope to be housed, and to take them out, they were pulled with ropes from the front while people pushed the airframe from behind. Around 1,000 entaigo were built nationwide, but most have collapsed or been demolished, so ones remaining in good condition like this are rare.

It's like an air-raid shelter for fighter planes. Before the war, this area thrived with munitions industries like Nakajima Aircraft, so it was a target of the Allies (US forces). Chofu Airfield was also built for that purpose.

Entaigo (aircraft bunker) A hangar to protect military aircraft from enemy air raids, built to preserve the few remaining, precious planes in preparation for the "Battle for the Japanese Mainland." From around Showa 19 (1944), as the Pacific War situation worsened, about 60 entaigo were built in a short period: about 30 concrete ones (covered) and about 30 U-shaped ones made of earthen embankments (uncovered). Construction was carried out mainly by the Army and construction companies, and many members of the local gardeners' association and middle school students were also mobilized. The entaigo and the airfield were connected by taxiways, and aircraft were moved by manpower with ropes tied to them. Around Chofu Airfield, 2 entaigo remain in Musashino-no-Mori Park and 2 in Fuchu City. The entaigo in Musashino-no-Mori Park are preserved as evidence carrying the memory of the war, as "storytellers for peace." [Excerpt from the on-site information board] I happened to pass by, spotted the 2 entaigo, and stopped by on a whim.

Built by the former Imperial Army to protect the Type 3 fighter "Hien" from air raids. From around 1944 (Showa 19), late in WW2, about 30 "covered type" bunkers like this and about 30 "uncovered type" were installed. Many entaigo can be seen in old aerial photos, but the only ones remaining today are two here in Osawa and one each in Shiraitodai and Asahicho to the southwest (the Asahicho one is privately owned and can't be visited). That they protected from air raids the very fighters meant to protect citizens from air raids can also be seen as the result of prioritizing preserving fighters for the "Battle for the Mainland" over protecting citizens from air raids.