US Navy tugboat shipwreck
The crew of the USS Conestoga poses for a photo. The ship vanished in 1921 after it left San Francisco Bay for Pearl Harbor.Naval Historical Center Photograph NH 71299

US Federal Maritime investigators have finally confirmed the discovery of a Navy tugboat 95 years after it sank shortly after leaving San Francisco Bay. Underwater cameras recorded eerie images of the tug lying largely intact with bunks, engine, boilers and a 50-caliber gun mounted on the main deck at the bottom of the sea about 30 miles (£48km) from San Francisco.

No human remains were seen. The disappearance of the USS Conestoga, with 56 officers and sailors on board, was particularly mysterious because it vanished during peacetime. It left the California shore for Pearl Harbor in Hawaii in March 1921, and never arrived. It was the last Navy ship in history to disappear in peacetime.

Investigators believe the tug simply became swamped by large waves in high winds and sank. The Conestoga, which was purchased by the railroad for service during World War I, had a reputation as a "wet vessel," meaning it was prone to taking on water in choppy seas.

"Weather logs indicate that around the time of Conestoga's departure, the wind velocity in the Golden Gate area" doubled and the "seas were rough with high waves. A garbled radio transmission from Conestoga relayed later by another ship stated the tug was 'battling a storm and that the barge she was towing had been torn adrift by heavy seas,'" said a statement by the US National Oceanic and Atmospheric Association (NOAA).

In 2009 NOAA investigators using sonar images located what appeared to be a tugboat in the waters close to the Farallon Islands near San Francisco. A full investigation began in 2014 and NOAA finally confirmed that it had found the Conestoga.

"After nearly a century of ambiguity and a profound sense of loss, the Conestoga's disappearance no longer is a mystery," said Manson Brown, assistant secretary of commerce for environmental observation and prediction and deputy NOAA administrator.

"We hope that this discovery brings the families of its lost crew some measure of closure and we look forward to working with the Navy to protect this historic shipwreck and honor the crew who paid the ultimate price for their service to the country."

The tugboat will remain exactly where it is. US federal law law prohibits the unauthorised disturbance of a sunken military vessel or plane.