Battery Cogan with two three-inch guns. Named in honor of a lieutenant in the 5th Continental Infantry during the American Revolution. Cogan, who had also been quartermaster of the 1st New Hamsphire Regiment, died August 21, 1778.
Battery Joseph Roswell Hawley with two six-inch pedestal guns. This battery also housed the fort's original observation station and electric equipment. Named in honor of Brigadier General Joseph R. Hawley who served with distinction during the American Civil War.
Battery Hardman with one six-inch pedestal gun. Named in honor of a Captain in the 2nd Maryland Regiment, Continental Army during the American Revolution. Hardman was taken prisoner at Camden, South Carolina and died while a prisoner of war on September 1, 1780.
During World War II, between 1941 and 1943, D Battery, 8th Coast Artillery protected Fort Baldwin and its Fire Control Tower that could radio the precise position of enemy vessels to batteries in Casco Bay.