There’s a great article on the history of the Red Hills Tunnels in today’s Honolulu Advertiser. 
Ted Vorfeld, who is an engineer, sent the link, along with some memories of the Red Hills Tunnels (which at one time were classified top secret by the U.S. government):
Uncle Charles Mullin took us through the place many years ago. He was in charge of PWC Pearl Harbor at the time. Then they stored Avgas and had automatically closing doors at each tank in case of fire. You had only about 20 seconds to evacuate the chamber after a horn blared, then the door closed and the chamber was filled with carbon dioxide.
In recent years I worked on a project to repair leaks and coat the bottom of these tanks. Extremely difficult to work on or in them. (To locate and fix leaks in the tanks, they fill them with water and float a raft on the water to work from.) Peter Schubert (one of my former partners at Thermal Engineering) also did a number of projects to fix the fuel lines in the tunnel.
The father of one of my Punahou classmates (Lynn Boerner) was one of the key engineers who helped build the facility: Charlie Boerner. Lynn lives on the Big Island and raises horses. Her mother still is alive and running an organic farm in Hana and we plan to visit her later this year. Charlie died in Hana a few years back when a farm tractor rolled over on him. He was 90+ years old at the time.
Dad claimed the workers were kept virtual prisoners to keep the construction a secret.
The houses in Foster Village all contained a “pipeline easement” in their deeds.
When I worked for the well drilling company that grandad Bill Mullin founded, I learned that the rock in Red Hill is volcanic ‘tuff’, a kind of compressed cinder material that is relatively soft (compared to basalt anyway).
Here’s the link to the Advertiser article, called Red Hill Hides WWII Engineering Wonder.
Just stumbled across this little article about Red Hill, and the storage tanks my dad Charley Boerner honchoed back in 1941. He was hired to come out all the way from New York State, on a two year contract to get those 16 story fuel storage tanks dug, and he was sworn to complete secrecy and had a high clearance at Pearl Harbor. Once the tunnels and tanks were done, Dad chose to stay on in the islands—forever—though World War II was heavilly underway. Dad was up atop Red Hill and watching the bombing at 7 am December 7th, and My Mom and I woke up to explosions —we were living in Naval Housing at Pearl Harbor, a few blocks from the water, with a view of the airfields and strafing. It is the second memory of my life, and still vivid, but that is another story. Thanks Chuck, and Ted, and whoever…..Red Hill is still pretty unknown, though it is no longer a Military Secret.