A captured Type 4 Kaiten torpedo on display in Hawaii. The torpedo resembled a small submarine, and could travel at speeds of up to 40 knots (46 mph), with a 3,000-pound warhead. (Wikimedia Commons/Prinz.W)

Japan’s ‘Kaiten’ Torpedo Was a Missile with a Person Inside

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Ironically, the addition of the human pilot—turning the torpedo into a seaborne kamikaze weapon—appears to have made it less effective.

During the opening years of the Pacific War, Japan operated what was arguably the world’s most lethal naval torpedo: the Type 93 “Long Lance,” which consistently outperformed Allied torpedoes in range, speed, and destructive power. The capability of the Type 93 caught Allied commanders by surprise, forcing adjustments during early naval battles.

Over time, US forces improved their torpedoes, while industrial shortages inhibited Japan’s ability to construct more of its own. The broader war turned against Japan as well, and after losses at Midway, Tokyo grew increasingly desperate to restore a naval advantage. One shocking, but unsurprising, innovation was to add a cockpit and pilot to the Type 93, turning it into a suicide bomb. The resulting Kaiten, or “Turning of Heaven,” was less well known than Japan’s kamikaze pilots—and ultimately far less effective in combat.

How Japan’s “Long Lance” Revolutionized Torpedo Warfare

In the early 20th century, the Washington Naval Treaty limited Japanese battleship........

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