Fort Stevens guarded the mouth of the Columbia River from 1863 to 1947 as Oregon’s main post in a Pacific harbor defense system. Begun as the Fort at Point Adams and renamed in 1865 for Isaac I. Stevens, it reflected concerns over the river’s vulnerability during periods of British-American tension. The post later expanded beyond its Civil War origins, including a U.S. Navy radio station and the secret Station S intercept operation that monitored Japanese naval traffic. Fort Stevens became nationally known when the Japanese submarine I-25 shelled it on June 21–22, 1942, the first enemy fire on a military installation in the contiguous United States during World War II.