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Researchers say they're closing in on Captain Cook's ship

FILE - In this April 17, 2005, file photo, the replica of the ship, the Endeavour, lies at anchor after it was removed from a sandbar in Botany Bay, Sydney. Researchers are set to announce on Wednesday, May 4, 2016 that they believe the original Endeavour is submerged somewhere in Rhode Island’s Newport Harbor. (AP Photo/Mark Baker, File)

FILE - In this April 17, 2005, file photo, the replica of the ship, the Endeavour, lies at anchor after it was removed from a sandbar in Botany Bay, Sydney. Researchers are set to announce on Wednesday, May 4, 2016 that they believe the original Endeavour is submerged somewhere in Rhode Island’s Newport Harbor. (AP Photo/Mark Baker, File)  (The Associated Press)

Researchers believe the ship that legendary explorer Captain James Cook used to sail around the world is still submerged somewhere in Rhode Island's Newport Harbor.

The Endeavour was part of a fleet of 13 ships the British scuttled during the Revolutionary War in 1778 to blockade the port.

The Rhode Island Marine Archaeology Project, which is leading the search effort, recently used a grant from the Australian National Maritime Museum to locate documents in London identifying the groups of ships in that fleet and where each was scuttled.

The nonprofit thinks the Endeavour is part of a group of five sunken wrecks.

It already has mapped nine sites in the harbor, including four of the five sites in that group.

It's announcing plans on Wednesday to investigate the fifth shipwreck this year.