Hart-Miller Island is an uninhabited Potomac River island in St. Marys County, Maryland, United States, that lies between the north and south channels of the river and has a length of less than one mile (0.8km). The state park’s namesake, John Mark Glenn Memorial State Park, is on the other side of the channel from Hart-Miller Island; however, it does not extend onto the island itself. Rather, the state park adjoins land which was formerly part of Calvert Cliffs Naval Station.
In addition to being small in size, the island is also relatively isolated; only two public boat launches are available, serving the upper and lower portions of the Potomac River, and there are no major roads leading to the island. As a result, visitation by tourists and residents remains low; according to local news reports, only 12 people visited the island in 2010. Nevertheless, the island plays an important role in the history of the Potomac River as the site where British Major John Andr met with American General Benedict Arnold in September 1780 to plot the surrender of West Point during the American Revolutionary War
On May 24, 2011, President Obama hosted a ceremony on the island to mark the 200th anniversary of its famous meeting. During World War II, the island was used as a gun emplacement for the defense of Washington, D.C., against possible invasion by German forces during the early stages of what became known as the Battle of the Capital. Two 16-inch guns were mounted on disappearing carriages, one near each end of the northernmost point of the island. Their ammunition magazines were built into the sides of these points. When the emplacements were completed, their huge shells would have been fired over the heads of any invading troops toward downtown Washington, D.C. Some sources claim that three such emplacements existed, but research conducted by the Smithsonian Institution found evidence of only two. One or both may have been removed before construction of Interstate 66 across the Potomac River, although they remain well preserved as a military landmark.
Visitors can see seven large blocks of concrete with holes cut out of them still in place along with parts of the foundations of the buildings they once guarded. Remnants of barbed wire fences and moats are all around the perimeter of the island. The entire area is fenced off and accessible to visitors only through guided tours. There are more than 20 miles (32km) of trails open to hiking throughout the park system, including 7 miles (11km) of trail on Hart-Miller Island alone. These trails connect with other areas like Woodrow Wilson National Forest and Big Pool Lake State Park. The 6-mile (9.7km) long “Arlington Loop” trail starts and ends in the city of Rockville. It travels past the Eisenhower Executive Office Building and stops at the Lincoln House Museum. Other popular routes include 3/4 Mile Run Trail and Kent Island Parkway Trail.
The park offers: