After the surprise Japanese air attack on Pearl Harbor nearly wiped out the Navy’s Pacific Fleet on Dec. 7, 1941, the United States declared war on Japan, as well as Germany, joining the European Allied force. As fear gripped a nation at war, many worried an enemy attack on America’s mainland was imminent. With tens of thousands of miles of exposed coastline, Naval bases and shipyards, part of America’s homeland defense tactics included establishing guard posts all along its shores.
An invasion never occurred, but the coast did face a deadly threat — German U-boats. The stealthy submarines operated off the entire U.S. coast, sometimes sinking ships within sight of the shoreline. Coastal batteries like Salisbury’s were intended to be used to shell U-boats. No U-boats were ever sunk in local waters.
According to fortwiki.com, military sites in Salisbury were established by the War Department in 1941 on land leased from the state of Massachusetts at two separate locations. Where the gunnery batteries are now exposed was the largest of the two locations, on 237 acres north of the entrance of the Merrimack River, south of the then town-owned Salisbury Beach. Its purpose was the first line of defense against enemy ships and the protection of the entrance to the Merrimack River.
The towers and guns were dismantled and the site returned to the state when the war ended. But the mounts remained, usually buried deep in sand.
The second military location was only about an 1 acre in size, in the residential area of the town beach, consisting of a fire control observation tower. According to northamericanforts.com, the site remained after the war ended, and was used by the state police until the structure was destroyed by a hurricane in 1958.
This second location was part of a series of stations for the Harbor Defenses of Portsmouth, where the Naval Shipyard was building warships. Other similar stations were placed on Plum Island and Crane Beach, but no remains exist today.