Establishment of Katashima Torpedo Testing Facility (1918)

Before delivery to the fleet every torpedo had to be test-fired to check its speed, course-keeping and depth-keeping. Torpedoes built at the Sasebo Naval Arsenal were originally tested at Maebata inside Sasebo Bay, but the decision to establish a dedicated torpedo testing facility at Kawatana was made in 1917, as the existing testing site at Maebata had become impractical due to heavy military and civilian maritime traffic.

The Katashima Peninsula, jutting into the relatively sheltered northern waters of Omura Bay — an inland sea joined to the open ocean only by narrow channels — offered an ideal location with adequate range for torpedo runs and minimal interference from shipping. Construction included a concrete artificial island firing platform approximately 50 meters offshore, linked to the land by a jetty, an observation post on the hilltop, and machine rooms for torpedo preparation. The air compression pump house, which charged the torpedoes' air flasks and was originally called the machine shop and torpedo adjustment shop, was completed in 1917. The facility began operations in 1918 (Taisho 7); its formal name was the Sasebo Naval Arsenal Kawatana Long-Range Torpedo Firing Range. First and second torpedo adjustment shops, a cooling water tank and an oil store were added later, and the two-storey brick observation post on the summit was used to watch the wakes of test torpedoes.

The range would serve the Navy continuously for 27 years until Japan's surrender in 1945. Katashima was originally a small island; in 1942 the water between it and the shore was filled in. During the Pacific War a naval arsenal and a torpedo boat training school were also established at Kawatana, making the town a centre for the production, testing and training side of the Navy's torpedo arm. After the defeat the range was abandoned; the buildings lost their roofs and were gradually overgrown.

Stone and brick remains of the firing platform, observation post and air compression pump house still stand on Katashima, and the ruins of a sonar acceptance test station lie offshore (closed to visitors because of the risk of slope collapse). Four structures — the observation post, the oil store, the machine room and torpedo adjustment room, and the five-arched jetty — are national Registered Tangible Cultural Properties. Kawatana Town laid the site out as Katashima Park in 2015, with a car park and footpaths.