Named after Civil War General Thomas H. Ruger and built in and around Diamond Head Crater, the fort was established by the United States for the purpose of defending the harbor of its newly annexed territory.
[5] The fort's prominent location on Diamond Head made it a natural fire control station, with several posts built into Lēʻahi Peak.
On the Kahala side is a larger stone gatehouse with rounded edges of the kind popular in the 1930s.
Between them, on the Kaimuki side, is a purely decorative structure, a circular stonewalled planter with two jagged stone arches intersecting at 90-degree angles.
It now stands at the edge of the Kapiolani Community College parking lot, but was once flanked by two large gun barrels.