In 1779 the
British adopted a strategy to seize parts of Maine, especially around Penobscot Bay , and make it a new colony to be called "New Ireland". The scheme was promoted by exiled Loyalists Dr. John Calef (1725–1812) and John Nutting (fl. 1775-85) and Englishman William Knox (1732–1810). It was intended to be a permanent colony for Loyalists and a base for military action during the war. The plan ultimately failed because of a lack of interest by the British government and the determination of the Americans to keep all of Maine.
In July 1779 British general Francis McLean captured Castine and built Fort George on the Bagaduce Peninsula on the eastern side of Penobscot Bay. The state of Massachusetts sent the Penobscot Expedition led by Massachusetts general Solomon Lovell and Continental Navy captain Dudley Saltonstall. The Americans failed to dislodge the British during a 21-day siege and were routed by the arrival of British reinforcements. The Royal Navy blocked an escape by sea so the Patriots burned their ships near present-day Bangor and walked home. Maine was unable to repel the British threat despite a reorganized defense and the imposition of martial law in selected areas. Some of the most easterly towns tried to become neutral. 
After the peace was signed in 1783, the New Ireland proposal was abandoned. In 1784 the British split New Brunswick off from Nova Scotia and made it into the desired Loyalist colony, with deference to King and Church, and with republicanism suppressed. It was almost named " New Ireland".
The Treaty of Paris that ended the war was ambiguous about the boundary between Maine and the neighboring British provinces of New Brunswick and Quebec. This would set the stage for the bloodless "Aroostook War" a half century later.