Nearly a century ago the Navy launched an extensive sea and air search off the Hawaiian Islands for a lost Navy tug with 56 crew members aboard.

The 170-foot coal-fired steamer USS Conestoga was heading from San Francisco to Pearl Harbor and was to continue on to American Samoa when it disappeared with its crew in 1921, never to be seen again.

In all, some 60 vessels, including the entire destroyer fleet at Pearl Harbor, including submarines, and two dozen aircraft, searched from May 2 to 13, according to the Office of National Marine Sanctuaries, part of the National Oceanic and Atmospheric Administration.

The ship’s fate has been one of the enduring naval mysteries of the 20th and 21st centuries. Some Navy officials assumed the Conestoga nearly made it to Pearl Harbor, hence the search off Hawaii.

Other evidence pointed to the ship possibly charting a wayward course in stormy weather and foundering off Manzanillo, Mexico.

“They found no trace of the tug, because it had sunk five weeks earlier and 2,058 nautical miles from Pearl Harbor,” the NOAA announced Wednesday.

In fact, the steamer likely foundered just over 40 miles from its departure point at Mare Island near San Francisco in the Greater Farallones National Marine Sanctuary as it struggled in “gale-whipped seas” to make anchorage in a sheltered cove, the marine sanctuaries program said.

The ship was located by chance in 2009, surveyed in 2014 and further identified late last year.

Some of the relatives of the lost sailors were expected to be at the Naval Heritage Center in Washington, D.C., today for the announcement, including Los Angeles resident Annika Cropper, grandniece of Mess Attendant 1st Class Edward Wilson.

Wilson was one of a handful of African-American crew members aboard the Conestoga when it vanished. Although 95 years separated family from the loss at sea, the resolution is appreciated by Cropper, who connected with other family members in the process.

“My grandmother was very close to Edward Wilson, her brother, so she passed many years ago, but I’m sure she never really got closure on what happened to her brother,” Cropper said in a phone interview. “So knowing that we now have closure for her, it means a great deal.”

She said her understanding is that African-Americans at that time were usually cooks in the Navy or had similar jobs, but she added she is proud that he served in the Navy in the 1920s.

The Maritime Heritage Program within the Office of National Marine Sanctuaries conducted some of its research through Ancestry.com and found Cropper’s cousin.

“I’ve met at least two new cousins — second cousins — through this,” Cropper said.

The loss of all hands on the Conestoga in the time period between World Wars I and II was noted by a newspaper account that ran a list of the “Conestoga martyrs.”

“The U.S.S. Conestoga which left Mare Island March 25, 1921, for Samoa by way of Pearl Harbor, has not been heard from since the day of her departure,” the newspaper reported. “The Navy Department has officially declared the vessel lost as of June 30, 1921. She disappeared from the face of the globe as completely as the U.S.S. Cyclops.”

The Cyclops was lost at sea in 1918 and has never been found.

Sadly, the Conestoga made it to within about 3 miles of Southeast Farallon Island as it sailed in heavy seas, leading to the loss of a tow barge, if there was one, and eventual swamping of the tug, the marine sanctuaries program concluded.

“The position and orientation of the wreck suggest to us that Conestoga’s officers and crew were steering the tug to get into more protected waters in the lee of the island or to reach the landing for the lighthouse station in Fisherman’s Cove,” the organization’s findings state.

Complicating the search was that the Conestoga’s loss, so close to its point of departure, had been unseen by anyone despite the proximity of the wreck to Southeast Farallon Island.

“It may have been dusk or dark, or no one may have been watching offshore on a windy day,” the report’s authors said.

According to the report, an inquiry to Pearl Harbor after the Conestoga was long overdue was mistakenly answered that it had arrived, but the Navy eventually expended “considerable effort to find the tug and its men.”

The Navy subsequently also looked at a derelict whaleboat discovered adrift 650 miles west of Manzanillo with a bronze letter “C.” A second big Navy search for the Conestoga was mounted along the Mexican coast by dozens of ships, another historical account states.

A NOAA sonar survey around the Farallon Islands in 2009 found a probable shipwreck in 185 feet of water. Three maritime heritage survey dives in 2014 with a remotely operated vehicle showed the wreck to be a steel-hulled, steam-powered oceangoing fleet tug. A follow-up survey in October provided additional proof the ship is the Conestoga.

The wreck, which lies on an even keel with a slight list to port, has been heavily colonized by marine growth, the marine sanctuaries said. The Navy ship’s 3-inch, 50-caliber gun on a World War I mount had fallen into the hull from the deteriorated main deck.

“The mystery of Conestoga’s disappearance has in part been solved. There will likely never be a complete understanding of why the tug foundered,” the Office of National Marine Sanctuaries said.

But “for the families, what is now clear is exactly where their relatives lie at rest, inside the tugboat where they paid the ultimate price for their service to country.”