Kawatana Naval Arsenal Ruins & Katashima Torpedo Testing Range

The Kawatana Naval Arsenal and Katashima Torpedo Testing Range occupy the tip of the Katashima Peninsula on the northern shore of Omura Bay in Kawatana Town, Higashisonogi District, Nagasaki Prefecture. This complex represents one of Japan's most significant surviving Imperial Japanese Navy torpedo-related heritage sites.

Establishment and Purpose

Prior to 1918, the Imperial Japanese Navy tested torpedoes at Maebata in Sasebo Bay. However, the bay's heavy military and civilian maritime traffic made torpedo testing increasingly dangerous and impractical. In 1917, the Navy decided to establish a dedicated testing facility at the relatively secluded Katashima Peninsula in Kawatana Town. Construction began immediately, and the Katashima Torpedo Testing Facility (片島魚雷発射試験場) commenced operations in 1918 (Taisho 7).

The facility's primary mission was to conduct performance tests, final inspections, and adjustments on torpedoes manufactured at three key production sites: the Sasebo Naval Arsenal (佐世保海軍工廠), the Kawatana Naval Arsenal (川棚海軍工廠, a branch of Sasebo), and the Mitsubishi Nagasaki Ordnance Works (三菱長崎兵器製作所). Torpedoes that passed inspection were forwarded to the Sasebo Naval Station for deployment with the fleet.

Facility Layout

The testing complex consisted of several distinct structures spread across the peninsula:

• Firing Platform (射場): A rectangular artificial island constructed from concrete blocks approximately 50 meters offshore in Omura Bay, with an area of 276 square meters. This is where torpedoes were actually launched into the bay for testing. The platform featured brick walls, reinforced concrete upper structures (three stories, with a floor area of 6.5 square meters per level), concrete roof slabs, and track foundations for torpedo handling.
• Observation Post (観測所): Located atop the peninsula hill, this building was used to observe and track torpedo trajectories (雷跡) after launch, recording performance data including speed, range, and accuracy.
• Machine Room and Torpedo Adjustment Room (機械室及び水雷調整室): These facilities handled the critical pre-launch preparation of torpedoes, including loading fuel and oxidizer, calibrating guidance systems, and making final mechanical adjustments.
• Rail Tracks: A network of tracks connected the various buildings, used for transporting the heavy torpedoes between preparation areas and the firing platform.

Torpedo Types Tested

Six types of torpedoes were tested at Katashima over its operational life. The most historically significant include:

• Type 91 Aerial Torpedo (九一式航空魚雷): Developed from 1931, this was the world's first practical air-dropped torpedo designed for shallow-water attack. It used unique wooden stabilizer fins (shed upon water entry) and an advanced angular acceleration control system. The Type 91 was the torpedo used by Japanese carrier aircraft in the attack on Pearl Harbor on December 7, 1941, and was mass-produced at the Kawatana Naval Arsenal during the war.
• Type 93 Oxygen Torpedo (九三式酸素魚雷, "Long Lance"): The most advanced torpedo of World War II, using pure oxygen instead of compressed air as an oxidizer. This gave it extraordinary range (up to 40 km), speed (48-50 knots), and a nearly wakeless track that made it extremely difficult for enemy ships to detect and evade. The Type 93's existence was unknown to the Allies for much of the war.

Wartime Expansion and Kawatana Naval Arsenal

As Japan's war effort expanded, Kawatana Town became a major naval industrial center. The Kawatana Naval Arsenal, originally a branch of the Sasebo Naval Arsenal, grew into a significant torpedo manufacturing facility in its own right. The facility experienced a burst of construction and modernization in 1938-39.

By 1944, as American air attacks intensified, school children were mobilized to excavate 16 tunnels into a nearby hillside for protected underground torpedo production. Remarkably, the U.S. Army Air Forces misidentified the Kawatana Naval Arsenal as a beer factory on their target maps, and the facility was never directly bombed.

After the atomic bombing of Nagasaki on August 9, 1945, casualties and burned citizens were evacuated to Kawatana by rail, and the Naval Arsenal's facilities were converted to accommodate and treat survivors, with female high school and junior high students serving as volunteer nurses.

Current State and Heritage Status

After the war's end, the facility was decommissioned and gradually abandoned. Forest has reclaimed much of the peninsula, leaving an atmospheric collection of concrete and brick ruins connected by dirt trails among the trees. Four wartime buildings survive among residential areas near the arsenal site, constructed from steel-slag bricks and red brick typical of 1930s military construction.

The offshore firing platform, observation post ruins, and machine room structures remain visible and accessible. Some passages, including the route to the newer observatory, have collapsed and are marked with safety warnings. The site was registered as a national Registered Tangible Cultural Property (登録有形文化財) on August 15, 2024, recognizing it as a nationally rare military heritage structure dedicated exclusively to torpedo testing.

The ruins are located within Katashima Park (片島公園), freely open to the public. The site serves as a Kawatana Shinyo Memorial as well, commemorating the young men who trained at Kawatana for shinyo (震洋, explosive motorboat) suicide missions in the war's final months.