Japan's army traces fatal Type 10 tank blast to debris left in the gun barrel

Investigators in Japan's Ground Self-Defense Force have concluded that debris left inside the gun barrel of a Type 10 tank most likely set off the shell explosion that killed three soldiers during live-fire training in April, according to Japanese media reports published on 6 and 7 November. The force is preparing to release the results of its accident inquiry before the end of the year.

Jiji Press, citing Defense Ministry officials, reported on 7 November that the burnt remains of the previous round appear to have stayed in the barrel and triggered the premature detonation of the next shell. Sankei Shimbun reported that an investigation committee set up at Western Army headquarters in Kumamoto had reached the same conclusion and judged that human error was unlikely to have caused the blast.

The accident happened at about 8:40 in the morning on 21 April at the Hijudai training area in Oita prefecture on the island of Kyushu. A 120mm high-explosive anti-tank round detonated inside the turret of a Type 10 belonging to the Western Army Tank Battalion, which is based at Camp Kusu. The tank commander, the gunner and a safety officer, all inside the turret, were killed, and the driver, who sat in the hull away from the turret, was seriously injured.

Mainichi Shimbun, which first reported the finding on the evening of 6 November, said six Type 10 tanks took part in the exercise and the tank involved had already fired several rounds. The Type 10 feeds shells stored in the turret into the gun with a belt-driven automatic loader, seals the barrel after loading, and is fired when a crew member presses a button. Defense Ministry officials told the paper that the round's casing is meant to burn away when it is fired but on rare occasions leaves debris behind in the barrel.

According to Mainichi, when the crew loaded a fresh round for the next shot, the incompletely burnt remains of the previous one reacted and set it off. The breech block, which closes the rear of the gun and contains the blast of firing, was not shut at that moment, so the force of the explosion entered the turret where the crew were working. Jiji also reported that the breech may not have operated normally.

After the accident the Ground Self-Defense Force chief of staff, General Masayoshi Arai, apologised to the public and suspended all live-fire training with Type 10 and older Type 90 tanks that use the same type of ammunition. He said at the time that he knew of no similar accident involving the Type 10. The reports this month did not say when or whether that suspension would be fully lifted.

The Type 10 is a domestically built main battle tank adopted in 2010 and made by Mitsubishi Heavy Industries. Mainichi reported that the force held about 120 of them at the end of the 2025 fiscal year, based in Hokkaido and at Camp Kusu in Oita among other sites. It is armed with a 120mm smoothbore gun with an automatic loader, along with heavy and medium machine guns.

The finding matters for Japan's ground forces because the Type 10 is the newest main battle tank in their inventory and the unit involved belongs to the Western Army on Kyushu. A cause rooted in how the ammunition burns and how the gun is loaded, rather than in crew error, points the inquiry towards changes in procedures, safety interlocks or the round itself across the whole Type 10 fleet, and the report due later this year should show which of those the force chooses.