Key point: A 1971 report has answers.

Point Sur is 600 feet of tough rock facing Pacific rollers that come 6,000 miles to pound the central California coast. Like the 19th-century lighthouse that marks the Point, the now-derelict compound of the former Naval Facility Point Sur evokes another era.

And it evokes a mystery — one involving secret underground naval bases, high-tech submarines and Cold War nuclear brinkmanship.

As late as the 1960s, Navy technicians and their families at Point Sur monitored undersea listening posts used to track Soviet subs. According to one legend, it wasn’t merely hydrophones the Navy ran from Point Sur, but submarines themselves based in giant man-made caverns dug into the rock.

There is something mythic and compelling about seashore scarps and naval bases — something drawing on archetypal imagery of treasure concealed in cave waters open to the sea. The ultimate supervillain’s lair, after all, is an island base with undersea access.

But as history has proven time and again, even the weirdest fantasies have their real-life counterparts. And those who dive for Atlantean gold sometimes surface with treasure. There really were — and are — some strange ideas deep down in the sea.

By 1966 the two surges into outer space and “inner space” were at their flood tide. While NASA gathered ever more momentum with monthly Gemini flights and a new Mission Control, the success of Sealab II and the CONSHELF III underwater habitat led to a presidential commission on oceanography and a bigger undersea commitment.

The Navy’s efforts to recover a lost hydrogen bomb off the coast of Spain that year and the loss of the attack sub USS Thresher three years before had brought new funding and discipline to deep submergence systems. In such heady times, dreams of colonizing the continental shelf within a generation seemed like sober predictions.

It was in this environment that C.F. Austin of the China Lake Naval Ordnance Test Station proposed the Rock-Site concept : manned undersea installations excavated into the rock of the seafloor. By applying well-understood principles employed for decades by the mining industry, Austin proposed that large bases could be constructed and operated anywhere suitable bedrock occurred in the ocean, at any depth.

Austin realized that even with mid-1960's technology, it would be possible to sink a wide shaft into the sea floor, seal and drain it, then use it as a staging area for further excavation. A tunnel-boring machine could be lowered into the shaft in pieces and then assembled to bore out more tunnels, including one for a small modular nuclear reactor much like those used at Camp Century in Greenland and McMurdo Base in Antarctica.

There’s very little hype in Austin’s report; the bulk of it is taken up with documentation of tunneling methods and mining operations conducted under the sea floor. These often follow seams and drifts underground as they continue offshore.

According to Austin, one Nova Scotia mine, Dominion Coal’s Cape Breton operation, consisted of “a complex of many consolidated undersea mines ranging in depth from 200 to 2,700 feet below the sea floor, with a water cover of 60 to 100 feet. These mines span an area of approximately 75 square miles and presently employ some 4,100 men in the undersea workings.”

Among the benefits of Rock-Site, Austin noted its immunity to weather and currents, its shirt-sleeve environment and its (very) controlled access. And Austin was not thinking small. “Structures within the sea floor can easily be made large and comfortable enough to permit the quartering of crews and their families for extended periods of time,” he wrote, “and can be made large enough to serve as supply and repair depots for large submersibles.”

Recent research on hardened missile basing concepts have proven various techniques for creating submarine-sized structures in hard substrates. The Air Force’s development of underground silos, subways and central commands produced real-world hardware and experience with construction techniques.

In the 1970s the Los Alamos National Lab investigated an atomic rock-drilling concept called the Nuclear Subterrene, which like Rock-Site sounds like something out of Johnny Quest, but also really happened. One wonders what might have happened had the Navy put its nuclear expertise to work drilling holes in the ocean floor.

The Rock-Site concept also bore much in common with NASA’s designs for underground moon bases. Very likely all three concepts — invulnerable bastions, space outposts and ocean bases — would have shared solutions to issues ranging from environmental control to crew morale.

Austin foresaw that Rock-Site bases could be ideal for industrial uses such as fossil-fuel production and deep-sea mining. In the decades since Austin’s study, industry has created the tools need to realize his vision. Though it’s not atomic-powered, the world’s largest tunnel-boring machine is about to drill a two-mile-long tunnel beneath Seattle wide enough to hold an Ohio-class sub.

One enterprising firm servicing the offshore renewables industry has designed a remote drilling rig for planting monopile anchors on the seafloor, while others are developing entire subsea electrical grids. Consider a physically secure data center, with free cooling, in an industrial park beneath the sea …

Did the Navy ever actually pursue the Rock-Site concept at Point Sur or elsewhere? A 1971 study discussed various methods of sea-floor excavation, but by then most man-in-the-sea development was classified. In the absence of information fantasy takes wing — er, fin — but nearly 50 years later C.F. Austin’s dream remains both sober and dazzlingly novel.

This article first appeared earlier this year.

Image: Reuters.