In the Last Days of World War II, Japan Fielded a Fleet of Kamikaze Mini-Subs

The Kairyu-class submarines were designed to protect the Japanese homeland from invasion.

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H.I. Sutton/Covert Shores

In the last months of World War II, with its massive navy defeated, Japan was desperate for a way to stem a possible Allied invasion on the horizon. The answer: building hundreds of kamikaze miniature submarines. Known as Kairyu, the sub carried two torpedoes each and were fitted with an explosive charge to ram and sink Allied ships and troop transports.

In 1945, defeat was at Japan's door. The four-year War in the Pacific had island-hopped from Hawaii to near Japan's “Home Islands.” Japan's flying kamikaze suicide pilots with their explosive-laden planes were one example of the country's desperation. The Kairyu submarines were another.

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H.I. Sutton/Covert Shores

Submarine authority H.I. Sutton, author of the submarine blog, describes the Kairyu submarines as just more than 56 feet long and four feet wide. The 19-ton submarines had a crew of two. The Kairyus could travel up to 450 nautical miles on the surface at 5.4 knots, or 38 nautical miles while submerged at speeds of 3 knots.

The Kairyu submarines were armed with two externally mounted torpedo tubes and a bow-mounted explosive charge for ramming. Like the kamikaze pilots of the air, Kairyu crews were not expected to return from their missions.

The Kairyus were meant to sink the Allied ships that would have been instrumental to an invasion. A likely tactic would have been to send out the Kairyu fleet as an Allied invasion force approached, sending the submarines deep to avoid detection. Once the invasion began, the Kairyus could surface among the enemy fleet and launch torpedoes. Many invasion transports, unloading troops and equipment, would have been unable to take evasive action. Once their torpedoes were expended, Kairyus would have then rammed allied ships.

History didn't turn out that way. The United States attacked with atomic bombs rather than an invasion, and Japan surrendered before the Kairyu fleet could be used. The Allies grabbed the surviving subs for study after the war. No country has built kamikaze mini-submarines since.

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