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 Australian National Maritime Museum to locate documents in London identifying the groups of ships in that fleet and where each was scuttled.
The non-profit thinks the Endeavour is part of a group of five sunken wrecks.
It's announcing plans today to investigate the fifth shipwreck this year.