"It was a clear day as I remember," recalled Engle, 77, a Honolulu resident and retired Navy captain. "We all knew what was happening was important."

The brainchild of Adm. Hyman G. Rickover, the father of the nuclear Navy, the Nautilus was like nothing that had ever sailed the seas. From the start, skipper Dennis Wilkinson and his submariners rewrote the record books.

"Until then the submarine was basically a surface ship that was capable of submerging," said Capt. Bill Hicks, director of Operations at the Navy's Pacific Submarine Force headquarters at Pearl Harbor. "It was very tied to the atmosphere. It had to come up and operate diesel engines to recharge batteries. It had limited submerged endurance."

The traditional diesel submarine could stay down at relatively shallow depths for a duration of two to three days at slower speeds of around 4 or 5 knots. If it went faster, the time it could stay submerged decreased drastically.

Nautilus was capable of traveling at speeds of more than 20 knots and remaining submerged for weeks or even months. From the moment it left Groton, the United States held a commanding lead in sea power — one it has maintained for half a century.

"I'm very confident in saying since the advent of Nautilus no nation has had a submarine force as capable as ours," said Hicks.

Still, there were growing pains.

A year and a half after the Nautilus took to the sea, it was dry docked because it had been experiencing vibrations at higher speeds. Initially, the problem was thought to be minor.

"We had this high-speed vibration when we ran at 20-plus knots," said Engle. "It was a light shaking — nothing horrible. But you'd sit in the ward room and see ripples in your cup of coffee. So, you wonder what's going on."

John Craven, soon-to-be chief scientist of the Navy's Special Projects Office at the time, led a team that tested the sub at sea. Those tests confirmed his fears that a design flaw in the ship's ballast tanks could have sent the Nautilus crashing to the bottom of the ocean at any moment.

"It would have sunk," said Craven, 80, of Honolulu, who compares the importance of Nautilus to the Apollo Moon landing. "Finding out what was wrong was the high experience point of my life."

Once discovered, Craven's team was able to correct the vibration problem and Nautilus and future nuclear subs went to sea with stabilized ballast tanks.

Around that same time, at the urging of Capt. Wilkinson, Engle wrote a thesis about a notion so fantastic it might have given Jules Verne pause — the feasibility of sailing a nuclear sub beneath the North Pole.

Then, in early August 1958, under Cmdr. William Anderson, Nautilus realized the impossible and its most historic voyage: following a layover at Pearl Harbor, Nautilus made the first crossing of the North Pole by a ship, cruising 400 feet below the pole. It sailed beneath the ice for 1,830 miles, surfacing in the Greenland Sea on Aug. 5.

That top-secret achievement signaled the beginning of an underwater Cold War contest with the Soviet Union that lasted decades. There followed numerous innovations and increasingly sophisticated submarine classes — Skipjack, Permit and Los Angeles.

Today, the Navy operates 72 nuclear submarines around the world, said Hicks. Pearl Harbor, the main submarine home port in the Pacific, has 17 Los Angeles class submarines operated by more than 2,500 submariners.

Soon, Pearl Harbor could be home port for the USS Hawai'i, a Virginia-class submarine, which will be commissioned in 2006.

Last September, at the U.S. Navy Submarine Force Museum in Groton, where the Nautilus now rests, Adm. F.L. "Skip" Bowman said, "I'm awestruck by the realization that so much of what makes our Navy today the most powerful on Earth can be traced right here to this very ship."

Bowman credited Nautilus and the nuclear pioneers who sailed it with being a major factor in America's Cold War victory over the Soviet Union.

Engle, who eventually commanded his own nuclear submarines, left the Nautilus before the North Pole adventure. From Nautilus, he went on to become an original crew member, or "plank owner," on the Skipjack, and then, in 1960, the Thresher. Engle left the Thresher after two years. On April 10, 1963, during the sub's very next voyage, the Thresher sank, killing all 129 aboard.

Although Engle can barely bring himself to discuss that tragedy, he agrees with Capt. Hicks that the safety record of nuclear submarines has been nothing short of incredible — 130 million miles traveled since the Nautilus without an accident involving nuclear propulsion.

"The Thresher and Scorpion were the two submarines we lost in the 1960s, and there was no nuclear accident involved with either of them," said Hicks. "Ultimately they both sank because of flooding."

As for the Nautilus, after 25 years and a half-million miles traveled, it was decommissioned on March 3, 1980, and is now a museum.

"The thing that Nautilus did was wake everybody up," said Engle. "It made it clear that nuclear power would let you stay under the water indefinitely, go fast, go slow, go deep, and do it quietly. To put it bluntly, Nautilus changed everything."