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Human Torpedo: Siluro a Lenta Corsa

by Robert Hansen

Siluro a Lenta Corsa Background

During WWII, Italian special forces of Decima MAS operated to great effect. The first modern naval commandos, they operated specialized equipment to execute strikes on high-value British targets. Under the cover of darkness, supply ships, destroyers, and even battleships fell victim to deadly attacks by Decima MAS. Of the pieces of equipment utilized in their attacks, the most iconic is the Siluro a Lenta Corsa.’ In English, the ‘slow running torpedo.’ Or, as it’s more widely known, the Human Torpedo. Known colloquially as the ‘Maiale’, or ‘pig’ among its pilots for its poor maneuverability. This device and its small crew had British sailors seeing enemy operators behind every shadow.

The Italian Human Torpedo required a two man crew.

The Italian Human Torpedo required a two-man crew.

Operational Roots of the Human Torpedo Concept

To the uninitiated, ‘human torpedoes’ may sound like a Soviet weapon from a kitschy Cold War-era film, but it’s not so literal. The Siluro a Lenta Corsa is a small craft, capable of carrying two operators and operating submerged. Its role is to infiltrate enemy harbors unseen, allowing the divers to detach the warheads. These warheads are set below the hull of an enemy vessel, where the explosion will deliver severe damage.

Related: Decima MAS: Italian Frogmen

The principle here is similar to modern torpedoes, which deliver a devastating explosion directly below their target. In perfect cases, the physical forces involved in the explosion will tear a ship in two. Throughout modern naval history, no one has developed an adequate defense to this method of attack. No wonder, then, that Decima MAS achieved such success in their operations throughout the Mediterranean.

Development of the “Maiale”

In 1935, naval officers, Teseo Tesei and Elios Toschi, initiated the Human Torpedo program from an idea Tesei formulated in 1927. However, Italy launched similar attacks employing midget submarines called Mignata, or “leech” in 1918 during the First World War. There, the concept showed promise and some success achieved while operating against the Austrian Navy. However, two factors prevented the advance of the project. One, the technology of the time presented a severe limitation, and two, the end of the war put an end to interest in it. Nonetheless, the SLC presents a powerful option for engaging enemy vessels without risking your own. With Italy facing the daunting prospect of naval war against Britain and her powerful fleet, an asymmetrical option was indispensable.

Teseo Tesei refined the concept of the Human Torpedo.

Teseo Tesei refined the concept of the Human Torpedo.

Capabilities of the SLC 100 Series

With a length of 7.3 meters, one meter in height, a beam of .533 meters, and a draught of .91 meters, the Siluro a Lenta Corsa possessed markedly small dimensions. The vessel weighed roughly one ton and was capable of 2.5 to 3 knots an hour while submerged. The Human Torpedo traveled at a depth of 49ft and could conceivably dive to 98ft maximum. Once dispatched from the carrying vessel, the SLC’s engine carried a range of 13 nautical miles.

Components of theSiluro a Lenta Corsa.

Components of theSiluro a Lenta Corsa.

The nose of the ‘torpedo’ mounted one to two warheads (one 230kg or two 125kg) and a one 1.6 hp electric motor. Once the two-man crew had successfully infiltrated the enemy harbor, they removed these warheads. After securing them to the bottom of the hull of their target, the divers could delay the explosion up to two and a half hours. This provided time for the divers to escape capture, and with any luck could cripple or sink the targeted ship.

Capabilities of the Siluro San Bartolomeo (SSB)

Design enhancements of the SLC Human Torpedo led to the Siluro San Bartolomeo (SSB), which was the last version of the SLC before the Italian Armistice.  The SSB addressed many of the shortcomings noted in the SLC. Only three units were ever made. Some main differences included the following:

  • Increased Beam to .799 m.
  • Two-man crew sat in the unit as opposed to on the unit.
  • Electric motor increased to 7.5hp.
  • Increased speed to 4.5 knots.
  • Warhead capacity increased to one 300kg or one 400kg or two 180/200kg mines.

According to the book Axis Midget Submarines by Jamie Prenatt and Mark Stille, the SSB was not only far superior to the SLC in terms of speed, range, maneuverability, and payload, but also more reliable. 

Human Torpedo Service History

While the soundness of the concept cannot be held in any doubt today, the results initially produced a reason for doubt. The ‘Maiale’ earned their nickname in over the course of the training of their crews, who found it difficult to control. Additionally, early models experienced teething issues and often sunk during testing. The initial combat deployments of the Siluro a Lenta Corsa left much to be desired. However, this generally was not due to any failure of the ships themselves. For instance, British aircraft thwarted early attempts at attacking Malta by strafing the submarines carrying the frogmen and their torpedo. Initial attacks on Gibraltar met mixed results, but those results soon improved.

Italian Frogmen of the Decima MAS prepare to strike on a Siluri a Lenta Corsa.

Italian Frogmen of the Decima MAS prepare to strike on a Siluri a Lenta Corsa.

The strengths of the manned torpedo outweighed their weaknesses; all that was left was a refinement of technique on part of their crews. By 1940, frogmen covertly based out of Spain regularly snuck into Gibraltar, attacked British vessels and escaped. In 1941, Decima MAS achieved their greatest success of the war. They struck a devastating blow against British naval power in the Mediterranean, disabling both British battleships in Alexandria Harbor. The trials and tribulations endured by the divers extolled the virtues and vices of the Maiale. Their small profile and stealth enabled them to penetrate the harbor defenses, but their poor reliability complicated the action. However, the attack still achieved tremendous success and delivered dominance over much of the Mediterranean to Italy.

Artist rendition of two Siluro a Lenta Corsa approaching a target vessel.

Artist rendition of two Siluro a Lenta Corsa approaching a target vessel. Image credit: Eigen werk PC. Paint Renegade.

Effectiveness of the Decima Mas

Throughout the course of the war, 30 of the SLC manned torpedoes saw service with the Decima MAS frogmen. While Decima MAS employed other vessels, the human torpedo was their most iconic and successful weapon throughout the war. In their attacks, the Decima Mas damaged and destroyed dozens of Allied vessels. Measured in tonnage, they damaged 130,000 tonnes of merchant shipping and 70,000 tonnes of military vessels.


Model Siluro a Lenta Corsa 100/200 Series
Crew 2
Length 23 ft 11.4" (7.3 m)
Height 3.2 ft (1 m)
Beam 1.75 ft (.533 m)
Weight (w/warhead) 3,500.9 lbs (1,588 kg)
Draught 2.98 ft (.91 m)
Powerplant One 1.6hp electric motor (1.2kW)
3 knots submerged
Armament (1) 230 kg or (2) 125 kg mines
Units Built 42 to 50
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