Japan finds likely cause of Type 10 explosion that killed 3 soldiers

Debris left inside the gun barrel of a Japanese Type 10 tank likely set off the April explosion that killed three soldiers during live-fire training in Oita Prefecture, the Mainichi Shimbun reported, citing Defense Ministry sources.

The Japan Ground Self-Defense Force is preparing to publish the results of its investigation as early as the end of this year.

The accident happened at about 8:40 a.m. on April 21 at the Hijudai training area, during a live-fire exercise by the Western Army Tank Battalion. A 120 mm (4.7-inch) high-explosive anti-tank round blew up inside the turret, the rotating armored compartment on top of the tank that holds the main gun and its crew. Three soldiers inside the turret died, and a fourth soldier standing away from the turret was seriously injured.

According to the newspaper’s sources, the problem started with the previous shot. The 120 mm anti-tank round uses a case that is meant to burn away completely when the gun fires, but in rare cases some of it can be left behind in the barrel. Investigators believe the earlier round did not burn completely and left residue in the barrel. When the crew loaded a new round to fire again, something in that residue reacted and set off the shell.

The breech, the heavy block at the back of the gun that seals the barrel and contains the blast when the gun fires, was not closed at the time, the sources said. With nothing to hold the blast in, it went back into the turret where the crew was sitting.

The Type 10 uses an automatic loader. Rounds stored in the turret are fed into the gun by a belt system, and after loading, the breech closes and a crew member fires the gun by pressing a button. Six Type 10 tanks took part in the exercise, and the tank involved had already fired several rounds before the explosion.

The accident is one of the deadliest training incidents for the Ground Self-Defense Force in recent years. When three Japanese soldiers were killed by the shell explosion inside the Type 10, the force halted live-fire training with the tank, and the deaths raised questions in Japan about whether the fatal tank blast could pause Type 10 orders.

The Type 10 is a Japanese-built main battle tank made by Mitsubishi Heavy Industries and adopted by the Ground Self-Defense Force in 2010. It is lighter than most Western tanks of its class and was designed with Japan’s mountainous terrain and narrow roads in mind.