Kōnoike Naval Air Base Ruins

The Kōnoike Naval Air Base (神之池航空基地, also romanized Kaminoike or Gōnoike) was a massive Imperial Japanese Navy installation built from 1941 near Lake Kōnoike in what is now Kashima City, Ibaraki Prefecture, and formally opened as a training air base in April 1944. Spanning approximately 500 hectares, it was a large naval air facility equipped with two main runways of 1,800 meters and 1,400 meters plus four auxiliary strips.

The second-generation Genzan Naval Air Group (元山海軍航空隊, also known as Wonsan Naval Air Group) was established on August 15, 1944, as an independent unit split from the Ōmura Naval Air Group's Genzan detachment. It took over the name and the airfield of the original Genzan unit that had been formed at Wonsan (元山) in Japanese-ruled Korea in 1940, and was a training unit for fighter pilots. Japanese sources place this unit at Wonsan, not at Kōnoike; the resident unit at Kōnoike was a separate training air group opened in April 1944.

As Japan's strategic situation deteriorated in early 1945, the Genzan Air Group was swept into the mass mobilization of training units for kamikaze operations. In April 1945, the group formed the Shichishō-tai (七生隊, 'Seven Lives Squadron') — a special attack unit whose name invoked the medieval samurai vow to serve one's lord through seven reincarnations. After the group's aircraft were ferried from Wonsan to Kanoya, Shichishō-tai pilots flew kamikaze sorties from early April until May 14, 1945 from Kanoya Air Base in Kagoshima Prefecture as part of Operation Kikusui, the massive aerial offensive against the Allied fleet at Okinawa.

The Kōnoike base itself served from November 1944 as the training ground for the 721st Naval Air Group (Jinrai Butai / Thunder Gods Corps), which operated the Yokosuka MXY-7 Ohka rocket-propelled suicide weapon. The base's facilities included dozens of concrete aircraft revetments (entaigō), of which only one covered example survives today at the nearby Ohka Park memorial.

On February 16–17, 1945, the base suffered devastating carrier-based air raids by US Navy aircraft, with approximately 130 planes attacking in nine waves, destroying most aircraft on the ground. Despite these losses, training and special attack operations continued until Japan's surrender on August 15, 1945.

After the war, the airfield was opened up as farmland for food production before being redeveloped from the late 1950s as part of the Kashima industrial zone. Sumitomo Metal Industries (now Nippon Steel Corporation) established its massive Kashima Works steel mill on the former base. Today, virtually no surface traces of the original military installation remain, though Ohka Park, on the edge of the steelworks grounds, preserves one revetment and a replica Ohka aircraft as a memorial to the base's wartime history.