To Fort Constitution's southwest, just in front of the fort visitor's parking area is Battery Elon Farnsworth. Built from 1897 to 1899 to mount two 8" Disappearing Guns, this battery was named for Brigadier General Elon J. Farnsworth (1837-1863), US Army, who was killed at the Battle of Gettysburg during the US Civil War.

Prominent in this picture is of course Mine Observation Station M1, which controlled a portion of Portsmouth Harbor's minefields through the Second World War.