A wreck-hunting organization located a sunken World War II submarine off the coast of Oahu.
STEP Ventures found the USS S-28, which sunk in 1944 with 49 crew members aboard during training, the Honolulu Star-Advertiser reported Thursday.
The sub was found in 8,700 feet (2,650 meters) of water.
The organization said the sub is "considered to be one of the most important lost ships in the central Pacific." It was found with autonomous underwater vehicles and a remotely operated vehicle.
The sub was in service during World War II. It initially was sent to Alaska to defend the Aleutian Islands against a possible Japanese invasion.
It sunk during training after making contact with a US Coast Guard ship. But a reason for why it sunk was never determined. Because of the depth, salvage operations were not possible, the Navy said.
"At no time during the approach or the ensuing sound search were distress signals from S-28 seen or heard, nor was any sound heard which indicated an explosion in S-28," the Naval History and Heritage Command said.
The armed forces' Court of Inquiry said the sub lost depth control "from either a material casualty or an operating error of personnel, or both, and that depth control was never regained. The exact cause of the loss of S-28 cannot be determined."
Data from the organization's find will be shared with the Navy to help determine the cause of the loss.