A fragment of a previously fired shell left behind in the loading position is believed to have caused the explosion of a round inside a tank at a Ground Self-Defense Force training range in Oita Prefecture in April, which killed three members, NHK reported.
The tank was on a training exercise when the shell burst inside the vehicle. The fragment is thought to have remained where a round is loaded, acting as a foreign object.
The finding points to a loading procedure that did not clear the chamber between rounds, a step meant to keep debris out of the breech during live-fire training.
The Ground Self-Defense Force has not announced further details of the investigation or any disciplinary action over the deaths.