250 years ago, Captain Cook and naturalist Sir Joseph Banks set sail in HMS Endeavour to find the rumored southern continent (of course, indigenous Australians had known about it for tens of thousands of years at that point). In 1770, the voyage arrived at Botany Bay, on the Australian coast, as part of three of Cook's famed voyages. He was killed in Hawaii during the last of them.

Cook's famous ship had a somewhat less-dramatic ending after it returned to Britain in the early 1770s. The Royal Navy sold her in 1775 to a private owner, and the ship that had once been a vehicle of exploration spent the first half of the Revolutionary War as a contracted troop transport and prison ship under the name Lord Sandwich. Then, in 1778, besieged British forces deliberately sank (or “scuttled” in nautical parlance) her, along with a dozen other ships, to help block the entrance of Rhode Island Harbor from French ships.

Now archaeologists with the Rhode Island Marine Archaeology Project, or RIMAP, say they’ve found her again, although they have more work ahead to demonstrate it.

Diving into a mystery

In 1993, archaeologists and divers consulted eighteenth-century maps and logs for information about the locations of the wrecks, then took to the water with side-scan sonar to find them. It was painstaking work, especially in the early years before GPS technology was available to help with precise mapping. Every possible shipwreck that turned up in the sonar images had to be checked by divers, a process archaeologists call “ground-truthing.” Some of those sites turned out to be modern vessels, lumpy geological formations, piles of abandoned commercial fishing tackle, and even Navy training torpedoes.

“The remote sensing technology that most people identify as marine archaeology has been only two percent of the work in Rhode Island. RIMAP divers and non-divers have done the other 98 percent,” says RIMAP in a post on its website.

By 2016, RIMAP’s volunteers, operating on grants and private donations, had located 10 of the 13 wrecks, almost exactly where historical charts said they should be. And the search had gotten a boost from the 1998 discovery of a 200-year-old paper trail linking the troop transport Lord Sandwich to its former life as HMS Endeavour. From that moment on, one of the big questions driving the search became “Which one is the Endeavour?”

According to RIMAP, “They all deserve careful investigation because of their importance to the history of the Revolution, but of course the international interest is in the possibility that RIMAP may find the Endeavour.”

Closing in on Endeavour

In a document that turned up in 2016, a British officer named Lt. Knowles listed the Lord Sandwich as one of the five ships he had scuttled to protect a coastal gun battery north of the island in 1778. Now, thanks to a combination of archival research and deep diving, archaeologists with RIMAP and the Australian National Maritime Museum have narrowed their search to a single shipwreck they say is probably the ship that once carried Cook and Banks to Australia.

Since eighteenth-century shipbuilders recorded the specifications of their projects in detail, archaeologists have spent some time on the bottom measuring the few timbers that remain buried beneath the silt and comparing those dimensions to what we know about HMS Endeavour’s construction. Because there is some historical information about where the Lord Sandwich was scuttled, archaeologists could also eliminate ships of the right size that weren’t in the right place, like a shipwreck dubbed RI 2119, which was briefly in the running last year.

Divers also collected samples of the wood from timbers on all five wrecks. Historical records list all 13 of the ships that were scuttled in 1778, and tracking those ships through trails of documents reveals that many of them were built in either India or North America, with timber from those places. But HMS Endeavour was built at a shipyard in the north of England, mostly of English oak, so oak timbers on a ship of the right size in the right place also provided a significant clue.

What’s down there?

There’s probably not much left of the ship itself. Any parts of the hull that weren’t quickly buried by silt would long since have decomposed in the water, leaving behind only piles of ballast (heavy stones placed in the bottom of a ship’s hold to help keep it stable when empty) visible on the harbor bottom. Beneath those piles of stone, though, artifacts and timbers buried in the silt may have been preserved. For most shipwrecks, that means archaeologists have a chance to recover the lower portions of the ship’s structure, usually with slightly more of one side than the other since the ship’s curved hull would have leaned as it settled on the bottom.

Even that fraction of the hull could help fill in some details about the ship’s history. Shipwrights made some changes to HMS Endeavour’s original structure when she was assigned to Captain Cook’s voyage; the ship had been designed as a coal-carrying collier. She may have undergone further remodeling for life as a troop transport, and some of those changes might be apparent in the remaining timbers.

When a ship was scuttled, her crew usually removed most items of value, from cannon and small arms to personal possessions and even some of the ship’s fittings. But a few things nearly always got dropped or forgotten in the rush, and archaeologists have found ceramic teapots, glass bottles, lead pieces from pumps, and bits of rope encased in concrete-like substances produced by corroding metal, all buried beneath the harbor’s silt amid the waterlogged timbers.

RIMAP says it hopes to begin an excavation by 2019.