Listed on the National Register of Historic Places, Fort Baldwin was built between 1905-1912 to protect the mouth of the Kennebec River. The river had long been strategically important as many industries came to rely on it; it also leads to the Augusta, the capital of Maine. It never saw action. At its height during WWI, 200 soldiers manned its three artillery batteries. It is the best example of a fort built during that time period in Maine. It was given to the state of Maine in 1924 after having been deemed unnecessary. However, it was manned between 1941-1943 during WWII.
http://www.maine.gov/cgi-bin/online/doc/parksearch/details.pl?park_id=86 https://en.wikipedia.org/wiki/Fort_Baldwin Frank A. Beard. "Fort Baldwin," National Park Service - National Register of Historic Places. 8-3-79.