The Torpedo Riders
The Decima, or "Unit Ten", were a deadly elite Naval Assault Group developed by the Italian government.
I. The Torpedo Riders
The Decima, or in English "Unit Ten", were an elite Naval Assault Group developed by the Italian government and used in World War II. They were officially known as the Tenth Light Flotilla of Assault Vehicles and became a forerunner of what would later be known in the US Navy as S.E.A.L. teams.
They carried out combat and covert sabotage missions by working in small groups of six to ten men. The Decima used newly developed technology such as early SCUBA gear called re-breathers, underwater demolitions and manned torpedos1 to strike their targets.
On these missions, the Nuotatori ("swimmers") were often mobilized from Torpedo Boats called MAS's or MTM's2 to deploy mines and guide specially designed manned torpedoes complete with instrumentation panels and steering wheels (see diagram below) into Allied targets. The manned torpedoes were known as Maiales ("pigs")1 or SLCs short for Siluro a Lenta Corsa meaning "Slow Soeed Torpedo".
The Torpedo Riders were a secret weapon of the Italian Navy. Their unit delivered mixed results during the Decima's combat operations.
A diagram of the Maiales, or Pigs, used as guided torpedos.
Due the Pig's build and bulk the slow nautical speed, (compared to unmanned torpedoes) swimmers were often spotted or could easily lose control of the weapon. Later versions, copied by the British were known as code name "Chariot". The Japanese used their version, the Kaiten, at least 100 times as a suicide weapon - using it to sink the USS Underhill on July 24, 1945 near the end of World War II.
II. Souda Bay and The Battle of Matapan
A Torpedo Armed Motorboat on a combat patrol during World War II.
The Decima were called into service in Mussolini's facist Italy in June of 1940. At the beginning of the World War II, they were used to covertly sabotage Allied freighters and attack ahead of large scale invasion forces.
In one of their most successful operations as a unit, the Decima were part of a series of attempts to attack Greece. The Italian Royal Navy's (IRN) actions to invade Greece took place in October of 1940 and in March of 1941. Except for the actions of the Decima in sinking freighters and the HMS York - the entirety of the Italian invasion attempts were total catastrophes.
In early March of 1941, ahead of a second doomed invasion attempt, Italian Decima frogmen were deployed to destroy Allied freighters to sink munitions and troops. They deployed mines and manned torpedos in Souda Bay an inland bay and shipping port that lies to the south of Greece in the north of the island of Crete. The Decima were acting ahead of the main IRN strike force that was sailing from Italy.
During it's part of the operation, the Decima severely crippled the HMS York, a heavy cruiser with a compliment of 630 men, by using two quick attack craft called MTM's2. They managed to rip open the aft compartments (located at the rear of the ship) with explosives killing two British sailors and dropping the York's keel to the bottom of the shallow Souda Bay.
Within hours of the arrival of the Italian strike force, they were decisively driven out of Greek waters in the Battle of Matapan. In some of the closest range firing between battle ships during World War II, three Italian cruisers, starting with the IRN Pola, IRN Fiume and IRN Zara and two destroyers, IRN Vittorio Alfieri and IRN Giosué Carducci were annihilated in a rout by Allied forces at sea.
Some 2,300 Italian sailors were killed. It should be noted that many Italian sailors would be rescued by Merchant Marines notified by a victorious Allied force. This was not a policy practiced by Axis naval forces who made it an unofficial policy to kill or abandon overboard Allied sailors at sea.
The only recorded damage to the Allied forces came when a single torpedo plane was shot down, killing it's crew of three, downed by the wounded Italian flagship, the IRN Vittorio Veneto.
The strategic and technical disadvantages, including no radar, no sonar and choosing to re-engage a superior force at night, played a large role in the utter defeat of the IRN at British and Greek hands.
However, one month after the humiliating loss for the Italian Royal Navy in it's attempt to invade Greece Nazi forces would take the country, in just 24 days, in April of the same year. In doing so, the way was opened for Hitler to invade Africa which he saw as a stepping stone for what became his own failed attempt to surround Europe.
III. Genius of Gibraltar
The Auxilary Ship Olterra appeared as decrepit hulk to all inspections during WWII.
Sabotage and small covert strikes were a method of slowing down naval shipments of troops and munitions travelling from Allied bases in Europe in World War II. To that end, many missions required a great cost of time, men and equipment to deliver a handfull of divers into Allied ports. However, one of the major strengths of the Decima was in it's ability to find ways around these costly and risky deliveries by establishing a covert base of operations to work from.
One example of this strategy involved a secret operation aboard the ship Olterra in the well-guarded Allied seaport of Gibraltar. The Italian tanker was docked in the critical shipping port and appeared as a salvaged hulk that was being retrofitted.
From a hidden series of chambers aboard this vessel, the Decima launched a campaign of mysterious torpedo attacks under the cover of darkness. The Decima secretly transformed the ship into a floating base of operations, adding diving chambers and munitions storage, while sinking Allied freighters using manned Mailales torpedoes and limpet mines from September of 1942 to August 1943 during the war.
The operation aboard the Olterra sunk 6 merchant ships totalling 40,000 tons (or 80,000 pounds) of war materials with a surprisingly low casualty rate on both sides. Only 3 divers and 3 sailors were killed due to surgical precision of the strikes and the timing of the attacks which were conducted at night when most of the freighter crews were ashore.
Another factor that allowed the operation to succeed so well is that when Decima teams were apprehended they never admitted to the base's existence. Instead, they insisted they were deployed from a submarine in the harbor. The universal penalty for sabotage during wartme is death yet under military interrogation Decima agents never gave up the Olterra operation. Members of the Italian secret service were rumoured to have scattered diving gear on the docks after attacks to further confuse authorities as to the origin of the sabotage.
The "Trojan Horse" ship ingeniously sunk freighters docked in Gibraltar.
After Mussolini's grip on power was first broken, in July of 1943, the Decima continued attacking freighters in Gibraltar. The Decima's role aboard the Olterra in the sinking Allied freighters was not discovered until after the war ended.
Soon afterwards, Spanish officials, eager to minimize any complicity in the Decima operation, tried to destroy the evidence. However, before they could intervene, three full Maiale model torpedoes were recovered aboard the Olterra after Italy surrendered in late 1943.
IV. The Italian Gestapo and Aftermath
Suspected "Ferruccio Nazionale" member hung in the streets during World War II Italy. The sign on his body read: "He shot at the Army of the Tenth".
As Italy's role in the Axis began to take a defensive role against the Allies, the Decima were given another mission: acting as an Italian Gestapo of spies and infiltrators into Anti-Fascist organizations within Italy. It's important to remember the Decima were the enemy of democracy and fought for fascism. They freely voiced Hitler's anti-Semitic views and Mussolini's lust for power in their unit and in the unit's publication "L'orizzonte" or "The Horizon"5.
They were notorious hunters of Partisan agents including communists and resistance fighters. In hunting for resistance members and Allied collaborators the Decima publicly shot and hung freedom fighters in the streets including a massacre of 68 suspected Partisans in Forno east of Turin in central Italy, during the war.
In all, the Decima were to be feared for their ingenuity. They employed a combination of skills using new technology and old stratagems on the battlefield. As facism began crashing in Italy they were re-purposed as secret police. Many of their members were sentenced to long prison terms during the Nuremberg trials after WW II only to be re-purposed yet again as secret agents for the forerunner of the American CIA the OSS (Over Seas Service) as spies6. The Decima's tools and tactics are used by military forces and scientific research communities, almost 70 years after their original implementation, in nearly every modern country today.
 = Manned Torpedoes were called Maiales meaning "pig" in Itailan and were guided by two-man teams. They were originally used in 1918 by the Italian Royal Navy against Austria to great effect.
 = The acronym for Motoscafo Armato Silurante (literally, Motorboat Armed with Torpedoes) or Motoscafo Anti Sommergibile (Motorboat Against Submarine) both mean "Motorized Torpedo Boat" in English and were also referred to as MTM's or MAS's.
 = A photo of a restored Maiales torpedo can be seen at Wikipedia Commons by following this link.
 = The Italian Duke of Spoleto is credited as the first to concieve of manned torpedoes. Major Elios Toschi and Major Teseo Tesei (Tesei was KIA at Malta in 1942 on a Decima combat mission) of the Italian Royal Navy later worked with the Italian goverment to develop the concept as a weapon of war.
 = This publication, with an article by Decima Commandant Junio Valerio Borghese about the "Occult Power of The Jew" has been re-published, in it's original format and in Italian, here.
 = OSS officer, and future CIA senior chief, John Angleton personally took "custody" of several former Decima officers, including Commandant Junio Valerio Borghese, to use as agents in America's Cold War against the USSR. The sentences of these Decima officers were never served.
Wikipedia, The Decima Flotilla
Italy at War, Decima MAS