And it was an accident. While plumbing the Pacific Ocean off the Hawaii coast, scientists discovered a 400-foot "Sen-Toku" class submarine that had been missing since 1946. The ship, which was one of the largest pre-nuclear submarines ever, was supposed to attack the Panama Canal but was sunk by the U.S. The sub, along with its sister ship found in 2005, could travel around the globe one and a half times without needing to refuel, and held up to three bombers that could take off shortly after the ship reached the surface. "While describing how they stumbled upon the vessel, researcher Jim Delgado said, "we came upon this as we were looking for other targets ... It is like watching a shark at rest." For a long time, the U.S. pleaded ignorant of the submarines they sank, supposedly to keep them from falling into the hands of the USSR.