Fort Stevens, along with Fort Columbia and Fort Canby (now Cape Disappointment State Park) in Washington comprised the Columbia River Harbor Defense System for the United States Army Coastal Artillery Corps to protect the entrance of the Columbia River from military threat.
Though they were each built at various periods in history they were collectively upgraded and maintained over the first half of the 20th century. Fort Stevens has the distinction of being the only military installation on US mainland to have been attacked in the Second World War when it was shelled by an Imperial Japanese* submarine on June 21, 1942. After the war the rationale for coastal defenses eroded and all three forts were deactivated in 1947.
* In June of 1942, bolstered by early tactical successes in the Pacific, the Japanese High Command ordered two submarines, the I-25 and the I-26, to patrol the west coast of North America. After the two submarines shelled Estevan Point lighthouse on Vancouver Island and torpedoed the Canadian SS Fort Camosun, the I-25 set course for Fort Stevens on the evening of June 21, 1942. The I-25 proceeded to open fire on the fort, though only hitting the beaches and causing some minimal damage to power and telephone lines. This attack gives Fort Stevens the unique distinction of being the only military installation on United States mainland to be fired upon during the Second World War.