Passengers said the USS Greeneville checked the ocean surface before ascending

Also in the area was the Ehime Maru, a 180ft training vessel from a Japanese fishery high school. It sailed from Honolulu harbour and was about halfway through a two-and-a-half month training voyage.

The Ehime Maru was hit and sunk by the 360ft submarine as it performed what is called an emergency main ballast tank blow.

Huge force

When this happens the submarine rockets to the surface at a steep angle.

A submarine performing an emergency ascent will break the surface with great force

The 7,000-tonne USS Greeneville would have risen out of the water with up to 60 feet of her bow showing before crashing down onto the ocean surface with huge force.

On board the submarine was a crew of about 130 - but also 15 civilian visitors. Two of them have said the crew made several visual checks of the ocean surface through the submarine's periscope before deciding to execute the rapid accent.

Video 'switched off'

The periscope checks were visible on a video screen inside the submarine but no-one apparently saw the fishing vessel.

Ehime Maru

Length: 180 feet Breadth: 32 feet Tonnage: 741 Speed: 12.5 knots Constructed 1996

A video recorder, which would have recorded images from the periscope, is said to have been switched off at the time.

The commander-in-chief of the US Pacific Fleet, Admiral Thomas B Fargo, is reported to have told members of the Senate Armed Services Committee he found it hard to see how the captain and crew of the USS Greeneville could have failed to notice the Japanese vessel.

Civilian at controls

One of the civilians on board the submarine was John Hall, a senior businessman. He said the captain asked him if he would like to pull the ballast levers, which would trigger the submarine's rapid ascent:

Civilian John Hall launched the submarine's accent

He said: "Sure, I'd love to do that." Mr Hall added that he pulled the levers on orders from the crew, and that a crewman then made sure the levers were in a locked position.

Mr Hall said he was told to sit down, and the submarine immediately began to rise.

It is not clear whether the submarine hit the Ehime Maru from beneath as it was breaking the surface, or if its bow slammed down on the vessel after shooting up and out of the water.

Mr Hall's description of the impact suggests the latter:

USS Greeneville

Los Angeles-class sub Length: 360 feet Breadth: 33 feet Tonnage: 7000 Armed with Tomahawk cruise missiles Commissioned in 1996 Home port is Pearl Harbor

"Just as it [the submarine] was starting to come down, and you could feel a sensation of it coming down, there was a very loud noise and the entire submarine shuddered," said Mr Hall.

A survivour on the Japanese vessel said it felt like being hit by a whale.

'Two great shocks'

Mr Hall also recalled the submarine captain's reaction: "I remember his words pretty vividly. He said, 'Jesus, what the hell was that?'"

The captain of Ehime Maru, Hisao Oonishi described how he experienced the impact. "I felt two great shocks all of a sudden. I looked back and saw the submarine surface."

Nine people are still missing after the accident

"Those people who were on duty on deck were rescued. But those who were inside the ship for rest or other reasons might have been left behind."

The Japanese vessel sank quickly after being hit. The US Navy and coast guard immediately launched a rescue operation.

They pulled 26 people from life rafts, some with minor injuries. Nine people are still missing, presumed dead.