Fort Stevens was an American military installation that guarded the mouth of the Columbia River in the state of Oregon. Built near the end of the American Civil War, it was named for slain Civil War general and former Washington Territory governor, Isaac Stevens. The fort was an active military reservation from 1863–1947.
The early earthen fortification.
Then the slightly later disappearing guns with lots of cement reinforcement.
And lot of WW2 improvements.
And a small but great museum
They mined the entrance to the Columbia River.
On the nights of June 21 and 22, 1942, a Japanese submarine fired 17 shells at Fort Stevens, making it the only military installation in the continental United States to receive hostile fire during World War II (the oil fields in Santa Barbara, California that were also shelled by the Japanese, was not considered a military installation). The attack caused no damage to the fort itself. The backstop for the post's baseball field was the only casualty. Fort Stevens and its gun batteries protected the river until shortly after World War II, and was decommissioned in 1947. All armament was scrapped and buildings went into auction.