The USS San Francisco, a Los Angeles-class attack submarine, arrived at its home port in Guam under its own steam Monday as the navy investigated the mishap.

A senior defense official, who asked not to be identified, told AFP initial reports were that the submarine was cruising at high speed at a depth of about 120 meters (400 feet) Sunday when it ran into an uncharted sea mountain.

Typically, a vessel's commander is held responsible for such mishaps, but the official said that might not be the result here if an investigation concludes that it was an uncharted sea mountain and the skipper's judgments were sound.

"Our hearts and prayers and sympathies are with the family of the sailor lost in that accident, his shipmates and all others injured and affected," Admiral Thomas Fargo, commander of the US Pacific Command, said in Hawaii.

"As we are still gathering facts, it would be inappropriate to speculate on the cause," he said. "But I assure you that the Pacific fleet will conduct a rapid and a thorough investigation and we'll let you know what happened once that investigation is complete."

The navy said the submarine's nuclear plant was not damaged and its hull was still intact.

But the sonar dome in the bow of the vessel was partly flooded during the collision, the official said.

The sailor who died Sunday of injuries sustained in the accident was identified as Machinist Mate 2nd Class John Allen Ashley, 24, of Akron, Ohio.

Twenty-three other crew members on the USS San Francisco were being treated "for a range of injuries, including broken bones, lacerations, bruises and a back injury," Petty Officer Alyssa Batarla told AFP.

The accident occurred on Friday, some 560 kilometers (350 miles) south of Guam, when the vessel was conducting underwater operations on its way to Brisbane, Australia with its crew of 137, the navy said.

All rights reserved. � 2005 Agence France-Presse. Sections of the information displayed on this page (dispatches, photographs, logos) are protected by intellectual property rights owned by Agence France-Presse. As a consequence, you may not copy, reproduce, modify, transmit, publish, display or in any way commercially exploit any of the content of this section without the prior written consent of Agence France-Presse.