The hidden tunnels of Diamond Head

Almost 3,000 people enter Diamond Head each day to walk up to the summit and admire the sweeping views of Waikiki. Most of them focus on the hiking trail, unaware they are in the midst of dozens of concealed military structures dating back to before World War I.

Diamond Head, also known by its Hawaiian name, Leahi, is honeycombed with about 20 hidden tunnels excavated into the crater’s lava and ash. The Army constructed the tunnels to hold everything from artillery pieces to underground rooms where Hawaii’s governor and lieutenant governor could be taken to keep the state running if there was a major military attack on Oahu or a natural disaster destroyed most of the island’s infrastructure.

While researching my book, "Secrets of Diamond Head: A History and Trail Guide," I was given permission to visit the off-limits tunnels.

During my childhood in the 1950s, the crater’s interior was off-limits to civilians. It was still an active Army base. Diamond Head was not opened to the public on a daily basis until 1978.

As a child living with my family on Kahala Avenue, I used to ride my bike up to Diamond Head on stealth missions to try to slip into the main tunnel unnoticed. I once tried to ride my horse into the crater, thinking the sight would so baffle the soldiers they would let me through. But none of my schemes worked. I was always kicked out.

Now I could go everywhere.

The construction of tunnels began in 1908 as part of the U.S. effort to turn Diamond Head into what The New York Times described in a 1914 headline as an "Armed Volcano … Part of our Pacific Gibraltar."

Diamond Head was a central part of the Fort Ruger Military Reservation, the Army’s first coastal defense fortification in the Hawaiian Islands. The main purpose of the military facilities was to look for enemy ships and destroy the vessels with mortars and artillery.

Even before World War I, Japan was believed to be the most likely enemy to attack Hawaii. Japan had defeated Russia in the Russo-Japa­nese War of 1905 and was in expansionist mode on an apparent path to eventually attack the Hawaiian Islands on its way to invade the U.S. mainland.

WITH ESCORTS from the state Department of Land and Natural Resources and the Hawaii Army National Guard leading me through the dark, dusty tunnels, I sometimes felt more like Indiana Jones in "Raiders of the Lost Ark" than a modern-day writer at the edge of the bustling tourist mecca of Waikiki.

In one tunnel we watched rats scamper on the ledges above as we investigated the rubble-strewn rooms with our flashlights.

Former state parks programs manager Clyde Hoso­kawa was usually my guide on my explorations. Members of the Hawaii Army National Guard led me on other forays.

Once, Hosokawa, some friends and I climbed up the steep western slope of the crater to a tunnel, which had been sealed for 40 years to keep out homeless squatters. After Hoso­kawa smashed open the lock and pulled back the tunnel’s rusting iron doors, we walked haltingly into the tunnel’s dry, clean air that had not been breathed by human beings for four decades.

Inside we found an empty bottle of a prescription psychotropic drug. We wondered where the drug-using cave dweller might be today.

The tunnel, built in 1920, had housed a searchlight, which could be moved outside on rails to light the night skies to scan for enemy ships approaching Hono­lulu.

I soon found other favorite tunnels. The Kapa­hulu or Mule Tunnel was close to the top of my list.

The Mule Tunnel was excavated in 1908 through the crater’s north wall. Back then it was the only way to get into Diamond Head. The Kahala Tunnel we drive through today to enter the crater was not built until 1943.

In the Mule Tunnel, mules pulled railroad cars filled with construction materials on narrow-gauge railroad tracks out into the center of the crater. The materials were hoisted up the side of the crater for construction of the Fire Control Station that hikers visit at the summit today.

The state Department of Defense and the American Red Cross, Hawaii Chapter, are the only agencies still using the off-limits Mule Tunnel. The Red Cross has office space where it stores emergency supplies in subtunnels dug into the Mule Tunnel’s west walls. The subtunnels were originally excavated for offices for the Hono­lulu Harbor Defense Command Post.

ANOTHER OF MY favorite tunnels is the M-O Tunnel, reached on a weed-choked, restricted road on the outer northeastern slope of the crater.

The M-O Tunnel is one of seven M (Munitions) Tunnels built in 1943. All are abandoned today, used primarily to store cardboard boxes of old government documents.

The U-shaped M-O Tunnel is special because it is the only tunnel in the M series built for human occupation. It was constructed to be a communications center. Still standing deep inside the tunnel is a rusting, old-fashioned telephone switchboard that formed the foundation of the Army’s communications network at Fort Ruger.

Batteries Hulings and Dodge on the east rim of Diamond Head are other great places to explore. Someday the former batteries may be opened to visitors, but today they are off-limits.

In 1915 the Army dug the tunnels to build Hulings and Dodge. Each battery had a pair of 4.72-inch, quick-firing Armstrong guns in fortified enclosures mounted on pedestals. The guns were designed to fire over Wai­alae and Kahala Beach to defend against possible infantry attacks.

The tunnels of Hulings and Dodge are used today only for storage.

Birkhimer — named after Medal of Honor winner Brig. Gen. William Edward Birkhimer — is another favorite tunnel. It is one of only two of Diamond Head’s hidden tunnels still used every day. The other is Battery 407, which the Hawaii Army National Guard uses as an emergency operations center.

When Birkhimer was built in 1916 on Diamond Head’s northeastern interior slope, it held four 12-inch mortars in a pit surrounded by a berm. Since then it has been remodeled many times.

Today, Birkhimer Tunnel is where Hawaii State Civil Defense officials gather to direct the state’s emergency response during natural disasters.

I hope that in the future some of Diamond Head’s tunnels will be opened to the public. They have a haunting power to remind us of wars past and a simpler time in Hawaii. The tunnels deserve to be so much more than storage rooms for discarded equipment and long-forgotten boxes of old government reports.

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Denby Fawcett is a longtime Hawaii television and newspaper journalist. Her new book, "Secrets of Diamond Head: A History and Trail Guide" (University of Hawai‘i Press, $20), is available in bookstores and at amazon.com.

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