In the inky depths of the Pacific's waters, a Japanese submarine on an infamous "Yanagi mission" slipped quietly toward its home port, cradling a secret cargo in its steel bosom.

It was on its way home from a Nazi-held port in France, where it had been loaded with advanced technology Japan hoped would restore its advantage in its war with the United States -- parts or plans for radar, jet aircraft, rocket engines, Enigma code machines.

But as the 1-29 passed 100 miles south of Taiwan, an American sonar operator aboard a U.S. submarine alerted to the enemy's presence prepared the aquatic echo that would target the enemy sub for American torpedoes. In the tense silence, he awaited for the go-ahead.

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"After several attempts the captain finally had it lined up," said Charles Nicolas, 92, the former sonar operator who now lives in Farmingdale. "He turned to me and said that he wanted one ping on this submarine."

"I gave him the one ping, which, if I remember right, was 1,250 yards," said Nicolas, who was awarded the military's Silver Star medal for his role in the sinking of the top-secret sub. "And as soon as he heard that, he fired four torpedoes."

"We could actually see the rising sun on the side of the submarine," said Nicolas, who raised three children in Jamaica, Queens, with his now-deceased wife, Rose, and retired in 1985 as a district manager for New York Telephone. "The rising sun, of course, is Japan's insignia."

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As the Allied dominance on the oceans and skies tightened during World War II, resources-starved Germany and Japan had begun relying on submarines to help each other by exchanging critical supplies, technology, medicines, expert personnel and even tons of gold.

These exchanges, known as Yanagi missions, included shipments of uranium, according to "The Japanese Submarine Force of World War II," by Carl Boyd, then a history professor at Old Dominion University.

Halting the Yanagi missions had been a Navy priority since they began in 1942.

The I-29's commander, Takakazu Kinashi, had dealt the U.S. Navy a humiliating blow aboard a different sub by sinking the USS Wasp aircraft carrier and fatally damaging the USS O'Brien destroyer during a 1942 engagement near Guadalcanal.

But more ominously, U.S. military leaders feared that a more coordinated effort between Germany and Japan could turn the war in favor of the Axis nations.

"With all of these things going to Japan, that completely freaked out the Americans," said Joseph M. Scalia, author of "Germany's Last Mission to Japan," which was published by the U.S. Naval Institute, a nonprofit military organization in Annapolis. "You have this rabid enemy in Asia that will die before surrendering and now they would get this technology?"

Naval intelligence had been able to track the 1-29 to where a three-member wolf pack of American attack submarines -- including Nicolas' boat, the Sawfish -- waited in the Luzon Strait, north of the Philippines.

But cornering the secret sub in the silence and the deep of the 200-mile-wide Luzon Strait would require that they surprise the I-29. Because sonar signals are easily detected by other submarines, the Sawfish's captain believed they would have but a single chance to bounce a sound wave off the I-29's distant hull, then hurriedly calculate the torpedo firing range before the enemy sub had a chance to react.

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The sonar technician he turned to was Nicolas, who had enlisted in the Navy four years earlier, and who volunteered for submarine duty because he thought surface ships were too large.

"It was very boring at times, day after day after day," he said of the monotony that had prevailed before the Sawfish spotted the I-29. "But then all of a sudden maybe one at night, or two or three in the morning, you hear "Clear the bridge . . . And then all hell broke out and you had enough action to last you in 10 minutes for the rest of the patrol."

Nicolas had handled important tasks before. In December 1941, he had been manning a radio watch aboard a different submarine near the Virgin Islands when he took a critical message that riveted the crew: Japan had attacked Pearl Harbor.

But in the Luzon strait, Nicolas, now a former chapter president of the U.S. Submarine Veterans of World War, was being asked to use his sonar skills to locate the most significant target of his career. He would need to target it with such swift efficiency that it would not have time to vanish into the Pacific's depths.

Nicolas was able to do so on his first try, allowing the Sawfish to send four torpedoes in rapid succession.

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Nicolas dismisses suggestions that he is a hero, even though his success in targeting the spy sub without alerting its crew earned him the military's third-highest combat medal.

"There were about 106 Japanese sailors who went down with the submarine, which in my way was vengeance for sinking the carrier Wasp," Nicolas said.

"Any one of the other sailors on board that submarine could have deserved that Silver Star," Nicolas said. "I just happened to be in the right position."