CASTINE – Visitors to Castine this summer will have a chance to step back 225 years into American history to what, some argue, is the worst naval defeat in America’s history.

Today the Castine Historical Society will unveil two exhibits related to the unsuccessful Penobscot Expedition of 1779, during which American forces attempted to retake the town of Castine from British troops.

A permanent exhibit will focus on the expedition itself, while the society’s summer exhibit will look at the aftermath of that battle, including the occupation of Castine by the British during the remainder of the war and the eventual departure of the Loyalists to St. Andrews, in what is now New Brunswick.

In July 1779, the Massachusetts General Assembly sent a fleet of more than 40 ships and 1,000 troops to drive out a smaller force of British troops that had landed in Castine the month before and started to build a fort.

After a two-week stalemate, the American naval forces, under the command of Commodore Dudley Saltonstall, planned to attack the British forces, which included just three vessels.

But informed that seven heavily armed British warships had sailed into Penobscot Bay, Saltonstall decided not to fight and instead fled up the Penobscot River where his entire fleet was sunk or scuttled and burned, most by their own crews in order to avoid capture by the British.

The defeat of the American fleet left the British in control of Castine and the entrance to the Penobscot River, an important access to the interior and the tall pine trees the British needed for masts, according to Jim Stone, the historical society’s education director. It also gave England a foothold on the Penobscot, which England envisioned as the boundary of a new Canadian province, called New Ireland. The little-known plan called for the Penobscot to form the western boundary of the province which would extend to the border of Nova Scotia.

The historical society’s two exhibitions will retell the tale of the Penobscot Expedition and its consequences for the Americans involved as well as the British Loyalists who occupied Castine at the time.

The permanent exhibit, the gift of Frank Hatch in memory of his father, Francis W. Hatch, will provide visitors with information about the battle through a short film and interactive video displays. It will be housed in the small alcove at the society’s Abbot School building that formerly housed the gift shop.

The area has been reconstructed by local woodworkers to resemble the day cabin of the frigate Warren, Saltonstall’s flagship for the ill-fated mission, Stone said. The new room even includes a slanted wall representing the stern of the ship with windows that will look out onto a scene of Penobscot Bay.

The exhibit, developed by Wood Spring Design Studio of Atkinson, N.H., is the result of more than three years of research, much of it done by Stone. It includes a facsimile of a chart table, complete with a video screen, which will feature a 15-minute narrated video about the expedition.

Society President Ann Miller said it has been exciting to watch the exhibit come together and she hopes it will attract visitors interested in American history.

“There is not one place that can hold all the material about the expedition,” Miller said. “There is a great deal of information. It’s surprising how much of it is available. We hope to make this a resource center for people who want to find out more about it.”

“Castine was the last British post to be evacuated,” Stone said. “They were here until April 1784. The Americans never came to accept the British surrender. They waited for them, but they never came.”

The opening ceremony will begin at 5 p.m. today at the Castine Unitarian Church next door to the historical society. It will feature a lecture on the Penobscot Expedition by William M. Fowler Jr., director of the Massachusetts Historical Society.

The exhibition will open for the season on July 1.