Some 71 minutes before a US submarine surfaced underneath a Japanese fishing boat, sonar crew on the USS Greeneville detected the Ehime Maru, which sank shortly after the collision, the Navy has told the US National Transportation Safety Board.
The board will conduct its own analysis of the Navy’s data to confirm that the vessel was indeed detected, and determine why the submarine’s crew later believed the area was clear when the submarine conducted an emergency rapid-ascent manoeuvre, board member John Hammerschmidt said yesterday.
The crewman responsible for tracking sonar contacts left his post within an hour of the collision because of the presence of 16 civilian guests in the submarine’s control room, Hammerschmidt added.
The fire control plotter is positioned in the control room and analyses the submarine’s speed, course, bearing and range of sonar contact.
But because of the 16 civilians in the control room, he had to stop doing that for a length of time Hammerschmidt did not disclose.
Nine crewmen and high school students remain missing following the sinking of the Ehime Maru off Hawaii on February 9. Twenty-six others were rescued.
Hammerschmidt indicated the sonar systems in the submarine and the crew who operate them will play a key part as the board tries to determine why the Ehime Maru was not detected before the sub began its rapid ascent.
"We are taking a very deliberate, very thorough, very comprehensive approach to this investigation," Hammerschmidt said.
He said the Greeneville gained passive sonar contact with a surface vessel at 12.32pm February 9 and designated the contact as Sierra 13. He said the Navy has reconstructed the path of the Ehime Maru and now knows that Sierra 13 was the Japanese ship.
Japanese leaders and families of the missing continued to press the US to raise the Ehime Maru, found Friday by a deep-sea robot in 2,003ft of water.