As rescuers continue to search for nine Japanese still missing after their fishing boat was sunk by a surfacing U.S. Navy submarine, officials are trying to understand how the accident could have happened.
Nine Japanese are still missing — four 17-year-old students, two teachers, and three crew members.
Twenty-six survivors were found stranded amid debris Friday, huddled in three life rafts.
The 499-ton Japanese trawler was carrying 35 people, including 13 high-school fisheries students and two teachers, when it was hit and critically damaged Friday by a 6,900-ton U.S. Navy attack sub about nine miles from Honolulu's Pearl Harbor, officials said.
The Japanese boat sank in just minutes, leaving only an oil slick, rafts, and scattered debris by the time Coast Guard rescuers arrived on the scene.
Navy officials have begun looking into the cause of the accident and today extended apologies to the families of the victims.
"While it's not yet clear how this accident occurred, it is both tragic and regrettable," said Adm. Thomas Fargo, commander in chief of the U.S. Pacific Fleet, at a news conference in Hawaii today. "I would like to express my apologies to all of those involved."
Sub Was Practicing an ‘Emergency Blow’
The USS Greeneville was off the northern Hawaiian island of Oahu, practicing a procedure known as a "emergency blow" when the accident happened.
In the maneuver, the submarine bursts quickly through the surface at a sharp angle. When practicing it, the submarine first comes to periscope depth, about 55 feet below the surface, and scans the area for nearby boats and ships.
When the area is determined to be clear of obstacles, the submarine dives to several hundred feet and levels off for a few minutes before coming up blind at a sharp angle.
Navy officials say the submarine caught the Japanese fishing boat right in the middle and ripped it in two.
The Japanese boat, Ehime Maru, was on a training exercise observing tuna stocks in the area, according to news reports in Tokyo. It was from the Japanese port of Uwajima.
The nuclear-powered submarine, which is armed with Tomahawk missiles, suffered only superficial damage. No one aboard the sub was hurt, according to Pentagon and the U.S. Navy.
Investigators from both the Navy and National Transportation Safety Board met the sub after the accident. They will seize the submarine's logbooks, any videotapes taken through the periscope and electronic records of acoustic noise in the water, as the first step in their probe into the incident.
Naval authorities have expressed regret and promised a full investigation.
The Ehime Maru was reported underway when it was struck, meaning its propellers should have been producing a loud and distinct pattern of noise recognizable to the Greeneville crew below.
"Leading into the accident, all that, will be investigated when the submarine returns to port," said Navy Lieutenant Commander Conrad Chun, the Pacific Fleet spokesman, in Honolulu. "It wouldn't be appropriate for me to speculate on the cause of this very tragic mishap."
Apologies From the U.S., Anger in Japan
President Bush and Secretary of State Colin Powell both have issued apologies and condolences.
"The United States extended its apologies and promised utmost efforts to find the missing," Japanese Prime Minister Yoshiro Mori said.
Senior officials there and the Japanese media are still calling for a full investigation.
Uwajima's families held out hope for the missing loved ones, and some relatives have headed for Hawaii. But for many, the initial shock gave way to despair and anger.
The missing crew members all came from the small fishing port in Uwajima, a hundred miles south of Hiroshima. The students aboard all went to the local fisheries high school. The exercise, which had been scheduled to last through March 23, to Hawaii was part of their training in deep-sea fishing.
Throughout the town, people gathered around televisions, anxious for more information.
"It's a bit chaotic right now," said Uwajima municipal official Masanori Mori. "There's a great deal of shock."
Among some Japanese, there already is distrust of the U.S. military because of a series of crimes by U.S. servicemen stationed in the island nation. The U.S. military has about 47,000 personnel in Japan.
On Sunday, a group of relatives, teachers and Uwajima officials plan to leave for Hawaii, to try to get answers about the accident.
ABCNEWS' Mark Litke, John McWethy, and ABCNEWS.com's Peter Hadfield in Tokyo contributed to this report.