This was the only mortar battery at Fort Stevens. At the time, mortars were considered the most lethal weapon in harbor defense. These stubby weapons fired shells in a high arc, shot gun style, with a goal of landing squarely on the deck of an enemy ship. Battery Clark was inactivated in late 1942; by then mortar fire was already too slow to reach the faster moving ships of World War II.
This six-story observation station served as command post and base end station for Battery Clark. Several range-finding instruments were located on the top floor. Observers shared information on enemy ship movements with the gun crews of Battery Clark. This helped the gunners fire more accurately.