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Ko-hyoteki class submarine

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General Characteristics
Displacement:46 tons submerged
Length:23.9 meters (78.5 feet)
Beam:1.8 meters (6 feet)
Height:3 meters (10.2 feet)
Ballast:5899 pounds in 534 11-pound lead bars
Designed Depth:30 meters (100 feet)
Propulsion:one electric motor, 600 horsepower at 1800 rpm, two screws conter-rotating on single shaft, leading prop 1.35 meters diameter, right-handed; trailing prop 1.25 meters diameter, left-handed
Batteries:192 trays of two two-volt cells each, 136 trays forward, 56 trays aft
Endurance:100 nautical miles at 2 knots, 80 nautical miles at 6 knots, 18 nautical miles at 19 knots
Speed:23 knots surfaced, 19 knots submerged
Complement:one commander, one crewman
Armament:two 18-inch torpedoes muzzle-loaded into tubes, one 300-pound scuttling charge (big enough not only to destroy the sub but to disable any ship it was near)
The ko-hyoteki (甲標的, "Type 'A' Target") class of Japanese midget submarines had no names, but were referred to by the designations of their "mother" I-16 class submarines, plus the suffix "tou" (艟). Thus, the midget carried by I-16 was known as I-16tou. They also had hull numbers beginning with the character "ha" (は), which can only be seen on a builder's plate inside the hull. They carried one commander and one crewman.

Twenty ko-hyoteki were built. The "Type 'A' Target" name was assigned as a ruse -- if their design was prematurely discovered by Japan's foes, the Japanese Navy could insist that the vessels were battle practice targets. The first two, Ha-1 and Ha-2, were used only in testing. Ha-19 was used as I-24tou (see below). The other hull numbers are unaccounted for.

On December 7, 1941, five ko-hyoteki joined the attack on Pearl Harbor, having been carried there by I-16, I-18, I-20, I-22, and I-24.

Photographs taken by Japanese aviators during the attack appeared to show a ko-hyoteki inside Pearl Harbor firing torpedoes at Battleship Row, but subsequent research has disproven this theory.

I-16tou, commanded by Masaji Yokoyama and crewed by Sadamu Uyeda, radioed on the evening of December 7 a report that the attacks had been successful, and was credited with the sinking of USS Arizona (BB-39), although in truth it was a high-level bomb dropped by a Kate from the carrier Hiryu that caused the sinking. The light cruiser St. Louis (CL-49) reported being attacked by torpedoes just outside the harbor but they impacted a coral reef and exploded short of the ship. As of December 2003, I-16tou has not yet been located.

I-18tou, commanded by Shigemi Furuno and crewed by Shigenori Yokohama, was depth-charged outside the harbor in Keehi Lagoon. The wreck was discovered in 1960 and raised. Its bow (with its still-dangerous torpedoes) was cut off and resunk, and the rest of the boat shipped to Japan. There, a new bow was fabricated and the boat put on display on Eta Jima.

I-20tou, commanded by Akira Hiro-o and crewed by Yoshio Katayama, was ordered to attack from a location closer to Waikiki than any of the other ko-hyoteki. Near their assigned location and before the air attack on Pearl began, the destroyer USS Ward (DD-139) reported firing on a submarine. In late August, 2002, the wreck of a ko-hyoteki was discovered with a three-inch shell hole in its sail. That shell must have killed Hiro-o, making him the very first enemy killed by United States forces in World War II.

I-22tou managed to make it into the harbor and fired a torpedo at the Curtiss (AV-4) that missed. Curtiss opened fire with her #3 gun and observed a hit on the conning tower. Shortly thereafter I-22tou was rammed and depth-charged by the Monaghan (DD-354), The sub was later raised and used as landfill at the sub base in Pearl Harbor with the bodies of commander Naoji Iwasa and crewman Naokicki Sasaki still aboard.

I-24tou (Ha-19) suffered mechanical problems and was captured the day after the attack. Its crewman, Kiyoshi Inagake, was killed, and its commander, Kazuo Sakamaki, was captured and made a prisoner of war -- the first for America. The sub was displayed throughout the United States and is currently at the National Museum of the Pacific War in Texas.

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