The second-in-command of the Japanese boat that was sunk by a US submarine says it is "unforgivable" that civilians were at the helm of the sub.
Nine people from the fishing vessel, four of them Japanese schoolchildren, are still missing and feared drowned.
Two civilians were at key control stations of the USS Greeneville when it surfaced under the Ehime Maru, sinking it.
"A civilian wouldn't know what to do," says Ryoichi Miya, first mate of the Ehime Maru.
"It's absolutely unforgivable if a civilian was operating it."
A Pacific Fleet spokesman would not specify the stations or release the names of the 16 civilians on board.
A defence official says on condition of anonymity that one civilian was at the helm, where the vertical movement and direction of the submarine are controlled.
The source says there was no indication that person played a role in Friday's crash.
"There were two civilians at two separate watch stations under the very close supervision of a qualified watch stander," says the source.
The submarine commander usually ensures nothing is overhead, but the Greeneville somehow failed to detect the presence of the fishing vessel.