IJN Submarine School (Sonar Training Hall Monument)

The Imperial Japanese Navy Submarine School (海軍潜水学校) was the sole institution responsible for training all submarine personnel in the Japanese fleet. Its history traces back to 1905, when Japan's first submarines — purchased from the United States — were initially stationed at Yokosuka. Within a year, operations were transferred to Kure due to the calmer waters of the Seto Inland Sea, establishing Kure as the traditional home of Japanese submarine training.

Formally established in 1920 with purpose-built school buildings in the Kure Naval District, the school initially used decommissioned submarine tenders moored at dockside as floating classrooms. It offered four main courses — General (普通科), Advanced (高等科), Specialized (専攻科), and Special Studies (特修科) — with an elite Type A course (甲種) later added specifically for training submarine captains. All courses were conducted in parallel tracks for gunnery/torpedo officers (兵科) and engineering officers (機関科).

In March 1942, as the war expanded, construction began on a new campus at the former Shinkoku Rayon factory site in Otake, approximately 30 km southwest of Kure. The Otake facility was established as a branch school on April 15, 1942, then promoted to independent school status on November 23, 1942, with a formal opening ceremony on June 7, 1943. The campus occupied roughly 66,000 m² (20,000 tsubo).

The school's most distinctive feature was the Sonar Training Hall (探知講堂, formally known as 電測水測講堂 — Electrical Detection and Hydrophone Measurement Lecture Hall). Built in 1942, this remarkable structure was supported by 15 reinforced concrete pillars extending directly from the seabed, with openings in the floor through which acoustic sensors could be lowered into the water. Trainees practiced identifying enemy submarines and surface vessels by their distinctive propeller signatures — a critical skill for undersea warfare.

In August–September 1943, the school conducted joint training exercises with German submarine crews, reflecting the Axis alliance's submarine cooperation. Meanwhile, the aging submarines formerly used for training at Kure were reorganized into the Kure Submarine Squadron (呉潜水戦隊).

As the war situation deteriorated, branch schools were established at Yanai (Yamaguchi Prefecture) for midget submarine (特殊潜航艇) training, and at Nanao (Anamizu, Ishikawa Prefecture) in spring 1945 after U.S. mine-laying operations made Inland Sea training increasingly dangerous.

The school closed on September 15, 1945, following Japan's surrender. The Otake campus subsequently served as a naval hospital supporting repatriation operations through Otake Port.

The original Sonar Training Hall stood in the sea until 2008, when land reclamation work for the Otake Port Industrial Park necessitated its removal. A section of the building's external wall was preserved and relocated to the Toei District Waterfront Green Park as a monument. The site in Kure where the original school operated is now occupied by the Japan Maritime Self-Defense Force (JMSDF) submarine base and the Submarine Education and Training Group (潜水艦教育訓練隊) — the direct institutional successor to the wartime submarine school.