With more time, military experts say, a fleet of revolutionary Japanese super-submarines could have changed the course of World War II.
Some were designed to launch bombers on kamikaze missions against New York City, Washington, D.C., and the Panama Canal. Others were thought to be twice as fast any other submarine used in the war.
None had the chance to execute their stealth missions against the U.S. mainland or critical targets in the Pacific during the war.
But after the war ended and the U.S. Navy seized and surveyed the vessels, it made a drastic decision: Each submarine was taken off the coast of Hawaii in 1946 and shot down to the ocean floor to keep the technology from falling into Soviet hands.
For years since, divers have scanned the depths of the Pacific to recover the subs and their technological secrets but to no avail.
A National Geographic Program premiering Tuesday documents a team of researchers' successful hunt for the super-submarines, which have not been seen by human eyes for more than 60 years.
Researchers Discover Two Scuttled Submarines
"This is one of the more significant marine heritage findings in recent years," Dr. Hans Van Tilburg of the National Oceanic and Atmospheric Administration's Office of National Marine Sanctuaries said in a statement. "These submarines are 60-year-old time capsules offering firsthand insight into a military technology that was far ahead of its time, so much so that if introduced earlier and in greater numbers, the submarines had the potential to turn the tide of war."
In a news conference last week in advance of the television premiere of "The Hunt for Samurai Subs," National Geographic Channel, NOAA and the University of Hawaii announced that the researchers had recently discovered two of the fleets' five submarines.
"These submarines were highly advanced and had very prominent targets," said Mark Fowler, the program's executive producer.
The I-14, which housed and launched two aircraft, was designed to launch attack bombers off the East Coast to target major U.S. cities. The I-201 fast-attack sub was twice as fast as any other submarine at the time.
Rare Video Footage Helped Locate New Search Area
"And the Americans … had no idea that they existed," Fowler said. "These were the first time any military had ever pulled off an aircraft-carrying submarine to this level."
Since 1992, researchers with the Hawaii Undersea Research Laboratory have been diving off the coast of Hawaii to search for the high-tech submarines.
In March 2005, Terry Kerby, the laboratory's submersible operations director, and his team discovered the first of the fleet, an I-401 aircraft carrier capable of traveling one and a half times around the globe and launching three strategic bombers.
But although they continued to scan the ocean floor near the first submarine, they could not locate the remaining four.
It wasn't until a new piece of information emerged that the team started to approach success.
Rare video footage of the Navy sinking the I-14 submarine in 1946, taken by a U.S. Navy chief, revealed a target zone the researchers had never considered.
"I look back on it today, I was some place nobody else was," Charles Alger, a retired Navy chief in charge of one of the Japanese submarines, said in the National Geographic program. "They got underway, got out to sea and then fired their torpedos. The front end tipped up, the back end tipped up and they each shot down to the bottom."
Researchers' Mission Included Many Setbacks
Using landmarks on the Hawaiian Island of Oahu, which is where Pearl Harbor is based, Kerby and his team were able to pinpoint the location where the submarines were submerged.
Piloting deep submergence vehicles, Kerby and colleague Max Cremer traveled 3,000 feet below the surface of the water to try to locate the scuttled subs.
Their missions were not without false alarms. On several occasions, the pair only found giant rocks where they hoped the sunken subs would be.
But, finally, they found what they spent more than a decade looking for.
"It is a great day," Kerby said during the successful mission. "Charles' footage paid off."
In his deep submergence vehicle, Kerby first flew over the deck of the massive 400-foot-long I-14 submarine, which housed and launched two military aircraft and could stay submerged for a month. He and Cremer also uncovered a sunken I-201 fast-attack submarine.
Naval Officers Surprised by Discovery
The discoveries surprised many people but perhaps none so much as the men who witnessed the moment the submarines were shot down.
"It was very sickening, the moment of the explosion," Alger said in the program. "But, like any good sailor, a job is done and we've done it."
"I never ever thought that it would ever be seen by a human being again."
National Geographic Channel's "The Hunt for the Samurai Subs" premieres Tuesday at 9 p.m. ET. For more information, click here.