Kashiwa Airfield & Shusui Rocket Interceptor Site

Kashiwa Airfield (柏飛行場) was an Imperial Japanese Army airfield established in November 1938 in what was then Tanaka Village, Higashi-Katsushika District, Chiba Prefecture (now the Kashiwa-no-ha area of Kashiwa City). Covering approximately 264 hectares by the end of the war, the facility featured a 1,500-meter runway and served various Army aviation units throughout the Pacific War.

By early 1945, the airfield had been designated as the primary operational base for Japan's most ambitious late-war interceptor program: the Mitsubishi J8M/Ki-200 "Shusui" (秋水, literally "Autumn Water" or "Sharp Sword"). The Shusui was a rocket-powered interceptor aircraft reverse-engineered from the German Messerschmitt Me 163 Komet. The German technical material was carried from occupied France by submarine I-29, which reached Singapore in July 1944 but was sunk by the USS Sawfish after leaving port with most of the documents still aboard. Japanese engineers had to work from the partial material flown ahead from Singapore by Technical Commander Eiichi Iwaya — a three-view drawing of the Me 163B, fuel composition tables and handling instructions, and a few test reports — and so could not simply copy the design.

The Shusui program was a joint Army-Navy project — an extreme rarity in wartime Japan where interservice rivalry was intense. The Navy designation was J8M and the Army designation Ki-200. Powered by a KR10 (Toku-Ro 2) liquid-fuel rocket engine burning a volatile combination of Ko-eki (甲液, T-Stoff equivalent: concentrated hydrogen peroxide) and Otsu-eki (乙液, C-Stoff equivalent: hydrazine hydrate with methanol), the Shusui was designed to climb to 10,000 meters in approximately 3.5 minutes at speeds approaching 900 km/h to intercept B-29 Superfortress bombers threatening the homeland.

The first and only powered flight took place on July 7, 1945, at Oppama Airfield (追浜飛行場) near Yokosuka, not at Kashiwa. Navy Lieutenant Toyohiko Inuzuka piloted the prototype, but the KR10 engine cut out during the climb due to a fuel supply malfunction. Inuzuka attempted to glide back to the airfield but clipped a building on the perimeter. He was critically injured and died early the following day. Seven J8M1/Ki-200 airframes had been completed by the war's end on August 15, 1945, but no further powered flights were achieved.

At Kashiwa, the Army Air Inspection Department's Special Weapons Unit (陸軍航空審査部特兵隊) had deployed from Tama Airfield to conduct ground tests, engine trials, and training flights using the unpowered glider variant "Akigusa" (秋草, Autumn Grass). Multiple underground fuel storage bunkers were constructed in two areas: adjacent to the airfield itself and approximately 3-4 kilometers away in the Hanano-i (花野井) and Omuro (大室) districts. These bunkers used prefabricated concrete Hume pipes as ventilation shafts above subterranean chambers built from stacked lightweight concrete blocks sealed with mortar, designed to safely store the extremely dangerous and corrosive rocket propellants separately.

Today, the former airfield site has been redeveloped into Kashiwa-no-ha Park (柏の葉公園), the University of Tokyo Kashiwa Campus, and various government research facilities. However, five underground fuel storage bunkers had been confirmed in the Omuro and Hanano-i districts (千葉県柏市大室・花野井) by 2010, with concrete ventilation pipes protruding from agricultural fields — often mistaken for abandoned artillery pieces by local residents. These are among the rarest surviving physical evidence of Japan's rocket aviation program and have been the subject of local surveys and preservation efforts.