http://www.latimes.com/news/nation-and-world/la-sci-minisub7-2009dec07,0,6991792.story
The remains of a Japanese mini-submarine that participated in the Dec. 7, 1941, attack on Pearl Harbor have been discovered, researchers are to report today, offering strong evidence that the sub fired its torpedoes at Battleship Row.
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“As soon as I saw the bow section with the distinctive net cutter, I knew that we had found the fifth midget sub,” Stephenson said. The Japanese navy modified net cutters on the subs for specific missions, and the one on the wreck was identical to those on the other mini-subs.
No torpedoes were found on the wreck, and evidence suggests that they were not present when the boat was sunk. A newly declassified photograph taken by a Japanese plane during the attack appeared to show a mini-sub firing a torpedo into Battleship Row. A report to Congress in 1942 by Adm. Chester W. Nimitz describes an unexploded 800-pound torpedo recovered after the battle. That’s twice the size carried by the torpedo bombers.
That torpedo was apparently a dud that missed the West Virginia.
But an examination of the remains of the Oklahoma shows that it apparently had underwater damage much larger than that associated with aerial torpedoes. An underwater blast would have caused it to capsize, Stephenson said. “Otherwise it would have settled to the bottom upright,” like the other sunken ships.