NBC News has obtained dramatic new details about the accident involving the U.S. Navy submarine San Francisco over the weekend that killed one sailor and injured 23 others.
Navy officials say the Los Angeles class submarine was cruising at approximately 40 mph at a depth of 525 feet Saturday when it slammed into an undersea "mound" about 350 miles southeast of Guam.
The impact of the collision slowed the 7,000-ton submarine from 40 mph to about 5 mph in an instant. Everyone standing on the bridge was violently thrown forward, NBC News was told. The crew member who died suffered fatal head injuries.
Immediately after the collision, the sub made an "emergency blow," or rapid ascent to the surface. It was during an emergency blow exercise that the U.S. submarine Greenville collided with a Japanese fishing boat, which then sunk off the coast of Hawaii, killing nine of 35 passengers.
The nose of the submarine, which contains the sub's sensitive sonar system, was destroyed. Despite the catastrophic collision, the inner hull of the sub remained intact, and the San Francisco limped into Guam. Had the inner hull been penetrated in the collision, Navy officials say the extreme pressure at 525 feet below sea level would have almost immediately crushed the sub.
Navy officials say the sub's commander said the San Francisco collided with an "uncharted" mound that would have been invisible to the sub's crew if they were running silently — without using underwater sonar. Some officials say, however, that the usual underwater sea lanes used by U.S. submarines have been fully charted and it's not clear why the sub, which was apparently in transit from Guam to Australia, would have been operating in waters that were not adequately charted.
It was unclear if the sub was traveling in a routine sea lane for submarines, which would have been thoroughly charted.
Navy investigators will have to determine the exact location and cause of the accident.
The dead man was identified by the Navy as Machinist Mate 2nd Class Joseph Allen Ashley, 24, of Akron, Ohio. He died Sunday of injuries he received in the accident, said Jon Yoshishige, spokesman for the U.S. Pacific Fleet in Honolulu.
There were no reports of damage to the USS San Francisco’s reactor plant, but the extent of damage to the 360-foot submarine would be determined after an investigation of its hull, Yoshishige said. The vessel reached port under its own power.
The San Francisco is one of three submarines based on Guam.
Located west of the international date line, Guam is a U.S. territory about 3,700 miles southwest of Hawaii.