A wreck-hunting organization announced that its search team has located the sunken World War II submarine USS S-28 in 8,700 feet of water off Oahu.

STEP Ventures said on its website that the S-28, which was lost with 49 crew during training on July 4, 1944, is “considered to be one of the most important lost ships in the central Pacific.”

“When the bombs fell on Dec. 7, she was being overhauled at Mare Island Naval Shipyard outside of San Francisco, Calif.,” the organization said. “She was one of several S-boats that were put into service in World War II and was initially sent to Alaska to defend the Aleutians against a possible Japanese invasion.”

STEP, which stands for Search for Those on Eternal Patrol, is made up of historians and explorers with a mission of discovering and documenting submerged maritime history. The organization said the expedition used autonomous underwater vehicles and a remotely operated vehicle to map and film the wreck, and that data will be shared with the Navy to help determine the cause of the loss.

The S-28’s was commissioned after World War I on Dec. 13, 1923, according to the organization.

The Naval History and Heritage Command said on its website that the sub got underway from Pearl Harbor on July 3, 1944, to conduct a week’s worth of operations. The vessel made two practice torpedo approaches on the Coast Guard cutter Reliance.

A day later while off the Waianae Coast the S-28 again carried out sonar exercises and made another practice approach on Reliance.

At 5:30 p.m. S-28 dove while about four miles from Reliance, according to the Navy. The Coast Guard cutter made sound contact with the sub, but at 6:20 p.m. at a distance of 4,700 yards, Reliance permanently lost sound contact with S-28.

“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 Court of Inquiry determined the S-28 sank shortly after 6:20 p.m. Because of the depth, salvage operations were not possible, the Navy said.

The court said the submarine 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.”

The “Lost 52 Project,” dedicated to the legacy of lost World War II submariners, also announced the discovery, which it said was made on Sept. 20.

“Based on preliminary video and other documentation,” the website said, “the team currently speculates that the sub suffered a hull failure that resulted in the eventual separation of the bow, causing a near instant loss.”

A release on the discovery said the expedition team was led by explorer Tim Taylor, president of Tiburon Subsea, and is Taylor’s third U.S. World War II submarine discovery. The team was supported by STEP Ventures, the release said.