Here’s what you’ll learn when you read this story:

• After the Japanese submarine I-52 sank during World War II, it would take more than fifty years before a determined historian finally located the wreck.
• The submarine had been carrying two tons of gold bars, which turned the search for its remains into a treasure hunt.
• The gold has remained elusive, but some parts of the submarine have been unreachable so far, and future expeditions may still find something glittering in the deep.

The Japanese Imperial Navy’s I Gō Dai Gojūni Sensuikan, or I-52 submarine, departed from Kure, Japan, en route to Nazi-occupied France on March 10, 1944. The submarine, codenamed Momi (which translates to “fir tree”), was set to rendezvous with a German U-boat near Lorient, and carried a cargo that included 2.2 tons of gold, which was meant as payment for technology that the Germans had equipped Japanese forces with.

Besides the gold—which would be worth over $100 million today—the sub had been carrying tons of tungsten and molybdenum, opium, and caffeine when it departed Japan. It also took on tons of quinine, raw rubber, and tin in the form of stamped ingots during a stop in Singapore before continuing on its fateful voyage, which was supposed to be an undercover operation. But unbeknownst to the Japanese, cryptologists had been decoding a classified map of the sub’s route, and knew exactly where it was headed. So, flanked by an escort of four destroyer escorts and a destroyer, the aircraft carrier USS Bogue headed for the mid-Atlantic to intercept the I-52. On board the carrier was a Grumman TBF Avenger torpedo bomber flown by Lieutenant Commander Jesse D. Taylor. After dropping a sonobuoy intended to identify submarine activity through sonar, he heard the unmistakable sound of a submarine propeller and deployed a torpedo.

“We had probably been airborne an hour to an hour and a half when Ed Whitlock, who was the radio operator, got on the intercom and told me he had a blip on his radar screen, so they honed in, and we dropped the parachute flares which spotted it,” Taylor said in a 2000 National Geographic documentary. “You were out to do your job, [which] was to sink a submarine if you found one.”

Other sonobuoys picked up signals from what may have been an underwater explosion close to midnight, and because the Americans were still uncertain whether they had indeed hit the Japanese sub, Lieutenant Junior Grade William Gordon dropped another torpedo. A massive explosion followed before the ocean went silent again, and what Taylor said next survives on a recording that can still be heard clearly through a haze of static: “We got that sonofabitch!”

When the destroyer USS Janssen approached the site of the bombing the next day, among the flotsam its crew discovered were scraps of silk, a sandal, tons of rubber, and scattered human body parts that were grisly evidence of a successful mission. But no gold was ever recovered from the wreckage, and for many years, the remains of the ship were as good as lost.

Following the sinking of the I-52, a man named Paul Tidwell spent decades trying to locate the vessel, spending countless hours poring over every relevant document he could possibly find. The Vietnam War veteran turned historian and shipwreck enthusiast scoured the Library of Congress, the National Archives, and several naval museums, going through thousands of pages containing ships’ logs and other records that could lead him to the site of the fallen submarine. In the National Archives, he found stacks of recently declassified documents that included intelligence reports and enemy radio messages that had been decoded, which finally pointed him in the direction of the lost ship—halfway between Barbados and the Cape Verde Islands.

While Tidwell (who is also a certified salvage diver) was after more than just the lost treasure, the prospect of finding more than 2 tons of gold on the ocean floor attracted investors, and by 1995, he’d raised over $1 million for an expedition.

As Tidwell scanned the seafloor from onboard the Russian oceanographic vessel R/V Yuzhmorgeologiya—which was chartered by marine contractor Sound Ocean Systems—he and his crew began to grow impatient as signs of the I-52 stubbornly refused to appear. Operations Director Tom Dettweiler decided to contact ocean discovery tech company Nauticos, and its founder and president, Navy veteran David Jourdan, proposed that the navigation records that Tidwell’s mission was using were off. Jourdan helped redirect the search, and on May 2, 1995, a ghost appeared in the deep—the I-52 had finally been sighted at around 17,000 feet, roughly three miles beneath the surface. After years of research, Tidwell had found his submarine.

But finding the wreck was one thing—reaching the gold was another. Three years later, Tidwell returned aboard the R/V Akademik Mstislav Keldysh (recognizable from its cameo in the movie Titanic), equipped with a trio of Mir deep-sea submersibles capable of diving to the wreck site. Initially, spirits were high. While parts of the hull had been smashed by the explosion, the submarine was recognizable, and most of its wooden planking remained intact more than fifty years after it had been sunk.

However, elation quickly dissolved into frustration as the trio of submersibles dove to search through the debris. One submersible discovered a metal box filled with opium. Submersible claws grabbed onto blocks of tin. Vestiges of human life still haunted the site (which has since been designated as a war grave), and though their remains may lie in parts of the submarine that have so far been unreachable, a solitary shoe humanizes those who were lost in the wreck. And Some chemical traces of gold in the sand near the submarine caught Tidwell’s attention. But despite all that was found, the 2.2 tons of gold have yet to resurface.

“I don’t want any part of I-52 unsolved,” Tidwell, who now owns the shipwreck recovery company Au Holdings, said in the National Geographic documentary. “I really want to get in there and record the inside and to do a recovery, and there’s more personal effects I’d like to recover [and have] returned to families.”

It’s thought that the darkest shadows of the submarine, which remain unexplored, could house the yet-unrecovered gold bars. But though the treasure (and some other remnants of the I-52’s cargo) still continue to elude Tidwell, he still hasn’t tired of searching for them.