[2] After Fort McKinley's closure, it was transferred to the United States Navy, which sold the site (via the General Services Administration) to private interests in 1961.

[3] The entirety of Cow Island was acquired by the government in 1873; Fort Lyon was built on 22 acres (8.9 ha) of it and was complete by 1909.

[3] A few buildings were built between 1905 and 1908, and a significant expansion to accommodate seven companies began in 1908-1909 and was largely complete by the end of 1910.

After the American entry into World War I in 1917, the forts were partially disarmed so the guns could be shipped to the Western Front in France.

[2] A history of the Coast Artillery in World War I states that none of the regiments in France equipped with 6-inch guns completed training in time to see action before the Armistice.

[3][8] In 1940-1941 both forts were expanded to deal with the influx of draftees; a draft was instituted shortly after the outbreak of World War II in Europe in September 1939 and the National Guard was mobilized, which included Coast Artillery Corps units.

This increased the post capacity to 62 officers, 18 married NCOs, 1438 enlisted men and 25 animals in Jun 1941.

[3] In late 1941 Fort Lyon added three new temporary buildings, a wharf, and utilities to house 130 enlisted men and 6 officers.

[10] Shortly after the war the Army withdrew from Forts McKinley and Lyon and the properties were sold or transferred.