Mystic and Avalon — the rescue submarines that waited at North Island.

At 9:13 on the morning of April 10, 1963, USS Thresher — the Navy's newest nuclear attack submarine, fresh from overhaul at Portsmouth Naval Shipyard — sent a fragmented transmission to the submarine rescue ship USS Skylark standing by on the surface and then went silent. She had been conducting deep-dive certification tests in the North Atlantic, 220 miles east of Cape Cod, with 129 men aboard: officers, enlisted crew, and civilian technicians from the shipyard. The Navy knew within hours where the ocean had taken her. What it could not do was reach her. The McCann rescue chamber — the steel rescue bell that had saved 33 men from USS Squalus after she sank in 243 feet of water off New Hampshire in 1939 — was built for the shallow coastal depths where submarines of an earlier era had tended to founder. Thresher lay at 8,400 feet. All 129 men were dead before the surface ships above them could accomplish anything beyond confirming the loss.

The institutional reckoning was systematic. By 1964, the Secretary of the Navy had established the Deep Submergence Systems Project, a directed program with a precise mandate: build rescue capability commensurate with the depths that nuclear submarines could now reach. The problem had a specific geometry. A nuclear attack boat of the era — a Permit-class or an upcoming Sturgeon-class — operated routinely at hundreds of feet of depth, and in a casualty might come to rest at twice that. Survivors, if the hull held and the flooding was contained, would have hours before the air supply was exhausted. No surface crane, no conventional diving bell, no rescue ship with existing equipment could reach them. What was required was a vehicle that could be transported by air to anywhere in the world within 72 hours, launched from a submarine mother ship at sea, and navigated in darkness to a hatch two thousand feet down against a running current, while a clock ran on the other side of the steel. The Navy gave the contract to Lockheed Missiles & Space Company in Sunnyvale, California.

What Lockheed delivered sat in an uneasy category between submarine and deep-sea probe. DSRV-1 — named Mystic — was accepted by the Navy in 1970 and commissioned on August 1, 1971. DSRV-2, named Avalon, was commissioned on September 1, 1972. Each was 49 feet long, built around three interlocked pressure spheres of high-yield steel: an aft sphere housing the propulsion system and silver-zinc battery banks, a center sphere for the three-person operating crew, and a forward sphere that served as the rescue chamber — fitted with seats and harnesses for up to 24 survivors. Four variable-pitch electric thrusters could drive the vehicle at four knots in still water and hold it against a three-knot current. The designed operating depth was 5,000 feet — well beyond the reach of any rescue system that had existed the morning Thresher went silent, and deep enough to cover the most plausible casualty scenarios involving the nuclear fleet the Cold War was building.

The deployment doctrine was built around the concept of the mother submarine — a nuclear attack boat specially fitted with an attachment cradle on its after deck. In an emergency, the DSRV would be loaded onto a C-141 Starlifter, or for longer reach in a single flight, a C-5A Galaxy, and flown to the nearest airfield to the disaster. From there it would be trucked to port, mated to the waiting mother submarine, and ridden piggyback beneath the surface to within range of the stricken vessel. At the rescue site the mother sub would hold depth while the DSRV detached and maneuvered on its own thrusters. When it had positioned over the escape hatch, the mating skirt — a rubber-rimmed, flared collar at the bow — would seal against the hull and the water between them would be pumped out. A hatch in the floor of the rescue sphere would open; survivors would climb through in pairs. The DSRV would return to the mother submarine, unload, and go back. Twenty-four people a trip, repeated until the submarine was emptied or conditions made further transfer impossible.

The urgency of the program was reinforced four years later. On May 22, 1968 — while the DSRVs were still in development — USS Scorpion, a Skipjack-class attack submarine, disappeared in the Atlantic approximately 400 miles southwest of the Azores with 99 men aboard. Her loss was never definitively explained; the wreck was located by October of that year at nearly 10,000 feet of water. Two nuclear attack submarines lost in five years, 228 men gone, neither crew reachable by any existing rescue system. The Cold War calculus was unambiguous: the Soviet Navy maintained its own rescue programs; the United States was building a matching capability. But the DSRVs existed to address a problem that, by definition, could only be solved once — and only if the casualty occurred at the right depth, in a locatable position, with enough air remaining when the rescue vehicle arrived. No exercise could validate that alignment. Only the event itself would.

Both Mystic and Avalon were assigned to Submarine Development Squadron Five — SUBDEVRON-5 — at Naval Air Station North Island on the Coronado peninsula, which closes the western approach to San Diego Bay. North Island brought together what the program required: the maintenance infrastructure of a major naval air station, access to deep-water piers where mother submarines could embark the vehicles, and a long runway capable of receiving the heavy transports needed to move a DSRV on short notice. Through the 1970s, '80s, and '90s, the vehicles cycled through regular exercises with Pacific Fleet submarines — certification dives off the California coast, mating drills against purpose-built docking targets, the constant rehearsal of a scenario that had never occurred. The crews, each vehicle operated by a small team of pilots and life-support specialists, maintained 72-hour airlift readiness as their core commitment. North Island became, without ceremony, the home of the deepest submarine rescue capability in the Western world.

The closest Mystic came to an operational rescue arrived not from a sunken American submarine but from a Russian one. On August 5, 2005, the Russian rescue submersible AS-28 — conducting operations off the Kamchatka Peninsula — became entangled in cables attached to a coastal surveillance array and sank to 190 meters with seven crew aboard. Russia's own rescue capability had been critically degraded in the years following the Kursk disaster of 2000, in which inadequate equipment and delayed acceptance of foreign assistance had turned a recoverable situation into a catastrophe. The Russian Navy requested international help. Britain, Japan, and the United States all began preparing assets; the U.S. Navy readied Mystic for potential deployment across the Pacific. Before she could be committed, a British remotely operated vehicle cut the entangling cables on August 7th and freed the submarine. All seven Russian submariners surfaced after approximately three days trapped on the bottom. Mystic was stood down. In thirty-four years of operational service, she never transferred a single survivor from a stricken submarine.

The DSRVs were built to answer a question nobody wanted to have to ask aloud: when the most capable submarines ever built sink in water where their crews might still be alive, what happens next? For three decades the answer was Mystic and Avalon, maintained on alert at North Island, rehearsing a rescue that never came — which is, in the logic of such programs, exactly what success looks like. The Navy retired Mystic in 2008 and replaced both vehicles with the Submarine Rescue Diving and Recompression System, a more portable capability that deploys without a dedicated mother submarine, continuing the obligation that Thresher's loss created. SUBDEVRON-5 still operates from the Coronado peninsula. Submarines still leave through the narrow channel between North Island and downtown San Diego, passing the same breakwater, disappearing into the same Pacific. The same deep water lies beyond it tonight that Mystic trained against for thirty years. The same channel. You could sail out past the jetty at dusk and watch a submarine go under.