75 years ago, life in the islands of Hawaii was changed forever. After decades of change, with the decline in numbers of the Native Hawaiian population and loss of the monarchy, becoming first a Republic and then an American territory, the people of the islands were hit with an even bigger blow when Japanese forces launched the infamous surprise attack on Pearl Harbor, on the island of Oahu.

The attack began in the early hours of December 7, 1941 when bombs, torpedoes, and machine guns devastated the naval base, killing more than 2300 people in less than two hours.

Aside from the airborne attack’s massive impact, one aspect of the attack was completely hidden from view. A very strategic move from the Japanese was the use of submarines in the attack. Luckily, the result wasn’t successful, but it certainly could have been.

The use of secretly built mini-submarines could have bee a completely devastating blow to the naval fleet, if it weren’t for a few small errors in judgement. The Japanese are believed to have used five mini-submarines, which were piggy-backed into close proximity of Hawaii atop full-sized submarines.

Japanese mini-submarines

These mini-submarines were a mere six feet wide and 80 feet long, and were powered by a 600hp engine. With this sort of power their travel speed was19 knots, which was twice as fast as the submarines that carried them to Pearl Harbor.

So what happened to these mini-submarines that stopped them from crippling the entire navy?

All five mini- submarines were released to approach their targets on the morning of December 7. Mini-submarine #1 was captured on the east side of Oahu. #2 was destroyed by a depth charge in Keehi Lagoon. Mini-submarine #3 was sunk by the USS Ward outside Pearl Harbor before it had a chance to fire any torpedoes. #4 fired two torpedoes, but both missed their targets and she was sunk by the Monaghan.

Mini-submarine #5 is now thought to have entered Pearl Harbor and fired her torpedoes, with one of them possibly hitting the USS Oklahoma. What happened to #5 after that was a mystery until recently, when she was found roughly three miles off the coast of West Loch, near Pearl Harbor.

Submarine 5

On May 21, 1944, seven landing craft exploded in West Loch. Since this disaster was kept completely secret, military authorities ran a major sweep of the area and anything on the seabed was retrieved and dumped about three miles out at sea. #5 was part of this clean-up.

If the Japanese forces had had a little more time for testing these mini-subs before late 1941, there is no doubt they could have had a much bigger impact in the attack at Pearl Harbor.

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