Nakoso Fu-Go Balloon Bomb Launch Base Site

The Nakoso Balloon Bomb Launch Base (勿来放球基地) was one of three coastal launch facilities established along the Pacific shore of eastern Honshu for Operation Fu-Go (ふ号作戦) — Imperial Japan's secret program to attack the North American mainland using unmanned hydrogen balloons carrying incendiary and antipersonnel bombs. Located in the Nakoso district of present-day Iwaki City, Fukushima Prefecture, it served as the base of the Third Battalion.

The Fu-Go balloon bomb (風船爆弾, fūsen bakudan) was conceived by the Imperial Japanese Army's Ninth Military Technology Research Institute (the Noborito Research Institute) in collaboration with meteorologists who had mapped the jet stream over the Pacific. Each balloon was approximately 10 meters in diameter, constructed from multiple layers of washi (traditional mulberry-bark paper) laminated with konnyaku (konjac) paste for gas-tightness. Filled with hydrogen, each balloon carried a payload of one 15 kg antipersonnel bomb and two or more 5 kg incendiary devices, along with an ingenious barometric altitude-control mechanism using sandbag ballast.

Three launch bases were established to exploit the winter jet stream: the First Battalion at Otsu (Ibaraki Prefecture, approximately 1,500 personnel with nine launch stations), the Second Battalion at Ichinomiya (Chiba Prefecture, approximately 700 personnel with six launch stations), and the Third Battalion at Nakoso (approximately 600 personnel organized into two squadrons operating six launch stations). The Nakoso site was selected for its Pacific-facing coastal position south of Sendai, proximity to railroad infrastructure (a supply spur was built from Nakoso Station on the Joban Line), availability of coastal sand for ballast, and terrain shielded by surrounding hills. Unlike the Otsu headquarters, which had its own hydrogen generation plant, the Nakoso base relied on hydrogen gas transported from factories around Tokyo.

The campaign opened on November 3, 1944, and continued through April 1945. Approximately 9,300 balloons were released in total from the three sites during the winter months when the jet stream was strongest. The balloons crossed the Pacific at altitudes of roughly 9,100 to 10,700 meters in some 30 to 100 hours. An estimated 300 to 1,000 reached North America, with confirmed incidents in 26 U.S. states, Alaska, Canada, and Mexico. On May 5, 1945, a balloon bomb killed six civilians near Bly, Oregon — a pastor's wife and five Sunday school children — the only enemy-caused fatalities on the U.S. mainland during the war.

Today, almost nothing remains of the Nakoso base. The launch pad areas, barracks, command post, and ammunition storage sites have been overtaken by vegetation or modern development including solar panel installations and road construction. The sole surviving physical evidence consists of two pairs of railway bridge abutments where the supply spur once crossed a small stream. The nearby Nakoso Seki Literary History Museum (勿来関文学歴史館) held a special exhibition on the balloon bombs and student mobilization from April to September 2024, featuring a one-tenth-scale balloon bomb model, a piece of balloon skin, and sketches and testimony from people involved in the operation.