The U.S. Army constructed Fort Canby, along with Fort Columbia and Fort Stevens, to defend the entrance to the Columbia River from enemy warships. U.S. Army troops manned the forts from the mid-19th century until the end of World War II. The specialized troops trained to respond to all possible threats from enemy warships. To do so, they operated high-powered weaponry that was the world's best and most modern technology of the times.