Longer than a football field, the Japanese submarine I-52 was carrying more than two tons of gold and hundreds of tons of other metals and raw materials to the Nazi war machine when it was sighted June 23, 1944, by Allied forces in the Atlantic.
An American torpedo bomber swept out of the midnight sky and dropped a torpedo. The pilot, listening to undersea sounds radioed by acoustic buoys, heard an explosion and a metallic groan as the submarine lost air and sank with more than 100 men.
For half a century the submarine lay hidden in the Atlantic, the exact location of its grave a mystery.
Until now. With the help of advanced gear and methods once reserved for the world's militaries, Paul R. Tidwell, a maritime researcher, found the hulk this spring more than three miles beneath the sea. He now plans to recover the gold, valued at about $25 million, and perhaps eventually to raise the submarine as well.
"It's amazing the condition she's in," Mr. Tidwell said. "There are no rivers of rust like on the Titanic," the British luxury liner that sank in 1912 and was discovered in 1985.
Finding the I-52 is a case study of how the deep oceans, once inaccessible, are being opened up for science and commerce.
During the Cold War, deep ocean technology was a monopoly of the superpowers and their navies. But Mr. Tidwell put together a team using an advanced research ship from Russia and special naval skills from America.
The team located the submarine in 17,000 feet of water about 1,200 miles west of the Cape Verde Islands, apparently intact save for a torpedo hole on her starboard side and some minor bow damage. She lies on rocky seabed, sitting upright.
The I-52 was part of a secretive exchange of materials and technologies between Hitler and Emperor Hirohito.
"Japan was desperate for German technology," said Dr. Carl Boyd, a military historian at Old Dominion University in Norfolk, Va., "and the Germans were desperate for raw materials."
Bigger than any American submarine of the day, the 357-foot-long I-52 was carrying 2 metric tons of gold, 228 tons of tin, molybdenum and tungsten, 54 tons of raw rubber and 3 tons of quinine. It also carried 109 men, including 14 experts from such concerns as the Mitsubishi Instrument Co., who were along to study and procure German technology.
The I-52 left Japan in March 1944 with the gold, then stopped in Singapore to pick up the other raw materials. In late April it set out again, traveling through the Indian Ocean and around Africa, bound for Lorient in Nazi-held France.
Unbeknown to Tokyo and Berlin, the I-52's route and cargo were known to the Allies, who had broken a host of Axis ciphers. Plans were laid for the ship's ruin.
On the moonless night of June 23, the I-52 rendezvoused with a German submarine in the mid-Atlantic. Food, fuel and two German technicians were taken aboard, as well as a radar detector meant to help the Japanese evade enemy planes as it neared Europe.
But it was too late. Jesse D. Taylor, a lieutenant commander flying as part of a naval task force, took off from the aircraft carrier Bogue in an Avenger bomber. Near midnight, just after the rendezvous, he picked up the I-52 on his radar.
Closing in, he dropped flares and two 500-pound bombs and watched as the submarine dove and evaded the attack.
Laying acoustic buoys over a mile of sea, Commander Taylor and his crew tracked the submarine. He then swooped out of the sky and dropped his only torpedo. A long silence was followed by a loud explosion.
Shipwrecks in deep water were once lost forever. But during the Cold War they slowly became reachable as American and Soviet navies developed gear for surveying each other's lost assets. Civilians started to reach the same depths only in the 1980s.
Mr. Tidwell, a maritime researcher, saw the glimmer of a prize in this emerging field in 1990 when he stumbled on recently declassified data about the I-52 in the National Archives while tracking wartime gold shipments.
Excited, he moved to the Washington area with his wife and two children and threw himself into discovering all he could about the submarine, eventually obtaining an official Navy estimate of the I-52's position. Along the way he raised $1 million from investors.
Mr. Tidwell hired a big Russian research ship, the Yuzhmorgeologiya, to hunt for the I-52 with sonars and cameras dangled on long cables.
To help run the expedition and refine the Russian sonar data, Mr. Tidwell hired Meridian Sciences Inc. of Columbia, Md., a Navy contractor skilled in teasing information out of a sonar signal.
Early this year, Mr. Tidwell found that a rival British group was planning to go after the I-52 as well. He offered to join forces. But the other group declined and began its search first. Despite its head start, the British group left the search area empty-handed.
Mr. Tidwell and his team set sail in April. His operations director was Tom Dettweiler, a Meridian staff member who had helped locate the Titanic. For two weeks the hunt was fruitless. The Yuzhmorgeologiya ran low on fuel and the search was almost abandoned.
Then, on May 2, a sonar reading produced a telltale dark sliver. Another pass with the sonar revealed the sliver to be a sunken submarine lying more than 3.2 miles down in international waters.
Mr. Tidwell says he is working closely with the Japanese authorities and has offered to return any personal effects and possibly the whole submarine, if raised. Mr. Tidwell noted that the Japanese tended to make no claims to lost riches and war booty.
All told, he said, recovery of the I-52's gold might cost $5 million to $8 million, leaving him and his investors a tidy profit.