The discovery of a huge Japanese submarine, 2,300 feet below sea level, off the southwest coast of O'ahu has finally put an end to the mystery of its whereabouts.

A team of explorers aboard the submersible Pisces V discovered the Imperial Japanese Navy's mega-submarine, the 'I-400,' on the sea floor off Hawaii in August.

At the end of World War II, the United States Navy captured a fleet of five submarines that included the 'I-400' in 1946. These submarines were among the last of the Imperial Japanese fleet.

Terry Kerby, the longtime operations director and chief submarine pilot for the Hawaii Undersea Research Laboratory (HURL) called the discovery "the real prize. This one actually trained for a mission: Attack the Panama Canal."

The megasub, which measures 400 feet, is nearly twice as long as a standard German U-boat of the time and was one of the "Sen-Toku" class submarines. Its remarkable feature was that it could serve as an underwater aircraft carrier. Plus, it could also travel one and a half times around the world without refueling.

"The I-400 has been on our 'to-find' list for some time," Kerby, veteran undersea explorer and leader of the expedition, said in a statement. "It was the first of its kind of only three built, so it is a unique and very historic submarine."

After these five submarines were captured at the end of the war, they were taken back to Pearl Harbor for inspection. Under the terms of the treaty that ended the war in 1946, the Soviet Union requested access to the submarines.

The U.S. instead decided to sink the submarines off, rather than handing over its advanced technology to the Soviet. They claimed to be unaware of its location. Four out of the five submarines have since been located.

 "More time could have been spent documenting them, but there was a Cold War beginning. It was important to get those subs on the bottom and keep them out of the hands of the Soviets. At the time this thing was sunk, it and its sister ship were the most advanced submarines in the world," said James P. Delgado, director of the National Oceanic and Atmospheric Administration's maritime heritage program and one of two marine archaeologists aboard the Pisces V, NY Times reports.