The Japan Maritime Self-Defense Force has determined that a fuel leak from a pipe joint in the engine room caused the fire that sank the minesweeper UKU SHIMA off the coast of Fukuoka in November 2024, resulting in the death of one crew member.
According to an investigation released on April 24, 2025, fuel leaked from a joint in the piping above the engine, dripped onto a metal cover over the exhaust pipe, and seeped into the heat-insulating material inside. The accumulated fuel then came into contact with the exhaust pipe, which reaches temperatures of about 430 degrees Celsius, igniting the blaze.
The fire broke out while the wooden-hulled vessel was en route to a training exercise in the waters off Munakata, Fukuoka Prefecture. The initial firefighting effort was led by a 33-year-old machinery room watchkeeper, who died during the response. Although the fire was initially believed to be under control, it reignited, forcing the crew to abandon ship and transfer to another minesweeper. The UKU SHIMA sank the following day, on November 11, 2024.
Investigators noted that the loss of electrical power shortly after the fire began significantly hampered firefighting efforts. Smoke from the blaze caused a short circuit in the generator room’s electrical panel, disabling remote controls for engine and fuel shutdown systems, as well as seawater pumps used for firefighting.
The unique construction of minesweepers like the UKU SHIMA also played a role in the incident. Because these ships are designed to avoid triggering magnetic mines, their hulls are often made of wood or non-metallic materials. This can make it challenging to detect residual heat or smoldering fires deep within the structure, potentially leading to premature declarations of fire containment.
Officials said the cramped layout of smaller vessels such as minesweepers limits the space available for backup power systems, which may have contributed to the inability to maintain critical systems during the emergency.
In response to the findings, the Maritime Self-Defense Force announced plans to implement preventive measures, including installing uninterruptible power supplies, modifying fuel piping to eliminate joints, and reviewing firefighting procedures for wooden-hulled ships.
Vice Admiral Yoshihiro Saito, Chief of Staff of the Maritime Self-Defense Force, expressed deep sorrow over the loss of Petty Officer Second Class Koga, praising his bravery and composure during the emergency. “He fearlessly confronted danger to fight the fire in the machinery room, and his calm, swift actions under extreme conditions exemplified a steadfast commitment to protecting his ship and shipmates,” Saito said.
