In January 1905, President Teddy Roosevelt instructed Secretary of War William H. Taft to convene the National Coast Defense Board (Taft Board) “to consider and report upon the coast defenses of the United States and the insular possessions (including Hawai‘i.)”
In 1906 the Taft Board recommended a system of Coast Artillery batteries to protect Pearl Harbor and Honolulu.
Between 1909-1921, the Hawaiian Coast Artillery Command had its headquarters at Fort Ruger and defenses included artillery regiments stationed at Fort Armstrong, Fort Barrette, Fort DeRussy, Diamond Head, Fort Kamehameha, Kuwa‘aohe Military Reservation (Fort Hase – later known as Marine Corps Base Hawaiʻi) and Fort Weaver.
The forts and battery emplacements batteries were dispersed for concealment and to insure that a projectile striking one would not thereby endanger a neighbor.
Fort Ruger Military Reservation was established at Diamond Head (Lēʻahi) in 1906. The Reservation was named in honor of Major General Thomas H. Ruger, who served from 1871 to 1876 as the superintendent of the United States Military Academy at West Point.
The fort included Battery Harlow (1910-1943); Battery Birkhimer (1916-1943); Battery Granger Adams (1935-1946); Battery Dodge (1915-1925); Battery Mills (1916-1925); Battery 407 (1944); Battery Hulings (1915-1925); and Battery Ruger (1937-1943).
According to the specifications called for by the Taft Board and subsequent updates, various guns and mortars were included at the various Batteries. These included 12″ Mortars, 8” on railway barbette carriages and other gun emplacements.
A network of tunnels was carved into the mountain and cannon emplacements were placed atop the crater rim along with observation posts and bunkers.
The fortifications within the Fort are all made of reinforced concrete and vary in size from the massive Battery Harlow and the four-story fire control station at the top of Leahi, to a dozen more modest six pound gun emplacements along the rim of the crater.
Battery Harlow is a massive reinforced concrete structure imbedded into the rear of Diamond Head. Built in 1910, it has three large bunkers which are separated by “courtyards” that served as platforms from which eight 12-inch mortars were fired.
Batteries Hulings and Dodge were completed in October 1915. These reinforced concrete structures tunnel through the wall of the crater and each contains one small room. The gun platforms with 4.7 inch guns are on the exterior wall of the crater.
Also dating from 1915 are a dozen 6 pound gun emplacements which are located along the rim of the crater. These are simple concrete slabs with eye rings which helped keep the weapons in place. These were installed to protect the batteries against ground attack.
Battery Birkhimer is located on the floor of the crater, near the rear. It also is made of reinforced concrete and primarily lies beneath the ground. Only its concrete portals are visible from the surface. Completed in 1916, this battery originally was armed with four 12-inch mortars.
Battery 407 was started in 1943 and completed near the end of World War II. Located on the front of Diamond Head, it has tunnels which go through the walls of the crater; it was armed with two 8-inch guns.
Battery Mills existed from 1916 to 1925 on the Kupikipikio Point Reservation on the lava point now known as Black Point and has long since been removed.
Battery Granger Adams (which replaced Battery Mills) was built there between 1933 and 1935, then decommissioned in 1946. Roads and houses now cover this area.
The four-story fire control tower located at the top of Leahi was built between 1908-1910. It is reached by a trail which terminates at the 560 foot elevation, then up a concrete stairway to a 225 foot long tunnel, finally a long concrete staircase of 99 steps leads to another tunnel which opens out on the south face of Diamond Head (with four levels of fire control stations.)
From this elaborate fire control station all the guns along the leeward coast could be commanded. The lowest level was for Battery Randolph at Fort DeRussy.
The next station above served both Randolph and Dudley at DeRussy. The third level commanded Battery Harlow at Fort Ruger and the top level was the battle commander’s station.
From this vantage point, 761 feet above sea level, the battle commander could view the coast from Koko Head to Waianae.
The conclusion of World War II and the advent of nuclear and missile warfare made the coastal batteries obsolete. Thus in December 1955 the majority of the land was turned over to the State of Hawai‘i.
Currently, Fort Ruger is down-scaled and part of the Diamond Head State Monument Park and is utilized for training and various administrative purposes by the Hawaii Army National Guard. Additionally, the installation is the presently home of the Joint Force Headquarters-Hawai‘i.
Battery Birkhimer has been recycled and presently serves as office space for the State Department of Defense. The other Batteries are generally used for storage.