‘A human torpedo?’ you may be asking. ‘Isn’t that suicidal?’

With the exception of the Kaiten, most human torpedoes are not literal torpedoes (in the military sense), but wet subs; essentially underwater motorcycles. Nevertheless, human torpedoes typically carry an explosive that the rider attaches to a large target, making them serious threats: like a mosquito, a human torpedo can be quite deadly for its small size. These vehicles were, above all, Axis products; the British Empire was the only Allied power to deploy any, and even their human torpedoes were based on Fascist Italy’s.

Human torpedoes were theoretical possibilities since the 1900s, and the first force to deploy one was the Regia Marina: it took out the Central Powers’ SMS Viribus Unitis in late 1918. There can be no doubt that this simple yet successful prototype laid the groundwork for more and better human torpedoes, but further work paused until the 1930s.

Quoting Jack Greene’s and Alessandro Massignani’s The Black Price and the Sea Devils: The Story of Prince Valerio Borghese and the Elite Commandos of the Decima MAS, pages 12–13:

Elios Toschi and Teseo Tesei […] each proposed a self-propelled craft based on the World War I assault device. Cavagnari accepted both proposals. Testing began on prototypes that would ultimately result in the two main attack craft used by the [Regia Marina] during World War II. They were the SLC, or Siluro a Lenta Corsa (slow torpedo), nicknamed the maiale (pig), and the MT (Motoscafo Turismo, or touring motorboats)—the official, somewhat deceptive name for the barchino.⁶

[…]

At the 1st Submarine Group near La Spezia, [Fascist] Italy’s main naval base, training took place for divers who had to exit from surface units and walk on the bottom of the sea towing charges like Paolucci’s leech. […] At the same time, beginning in September 1935 the 1st Submarine Group began to produce prototypes of the SLCs developed by Toschi and Tesei. […] In October 1935, the prototype was ready. Despite several small construction defects, it proved to work surprisingly well both in a swimming pool and at sea, so a second SLC was ordered. It was built quickly and was ready by January 1936.

[…]

The work of Tesei and Toschi went on until the summer of 1936; the campaign in Ethiopia ended in the late spring and the international situation improved, although the League of Nations had inflicted economic sanctions on [the Kingdom of] Italy. The fact is that the league and the Great Powers had been faced with a fait accompli and were still not fully ready to check the threat of [European Fascism] and Japan[ese Imperialism].

In any case, the prototypes were stored and forgotten until the Czechoslovakian crisis of 1938, although some documents show interest by officers in this assault weapon in 1937. Cavagnari’s cavalier attitude toward the Mezzi Insidiosi, or naval guerrilla war, would be a crucial failure that would help ensure [the Kingdom of] Italy’s maritime defeat by the Allies in 1940.⁸

Notice how work on the assault craft slowed down and sped up depending on the larger context: work accelerated during and shortly before warfare, but decelerated when the situation was under control.

Maiale’s success inspired not only the British Empire but also the IOF and the Kriegsmarine, although its influence on the Kriegsmarine was, oddly enough, indirect. Quoting Lawrence Paterson’s Weapons of Desperation: German Frogmen and Midget Submarines of World War II, pages 2–3:

Although the SLC was not the only weapon in [the Regia Marina’s] midget arsenal, explosive motor boats also having already made their presence felt with successful attacks on British warships, it was the human torpedo that particularly captured imaginations elsewhere. Originally envisaged by the [Regia Marina] for use in clandestine attacks on enemy harbours such as Alexandria, Valerta and Gibraltar, five planned operations had already failed before de la Pene’s success.

However, the Royal Navy were suitably impressed and formed their own group — the Under Water Working Party (UWWP) — to study the idea. In less than a year their own version of the SLC, named the ‘Chariot’ by the British, was in service and plans were made to attack the [Axis] battleship Tirpitz in Trondheimsfjord, Norway.

Eventually, this operation failed as the two Chariots towed by trawler to within range of the [Axis] behemoth broke free from their host and sank before they could be deployed. However, elsewhere in Palermo and Tripoli, Italian and German shipping respectively were successfully attacked and sunk.

With the capture of the ‘Charioteers’ their modus operandi was revealed to the [Kriegsmarine], Admiral Dönitz paying particular attention to their use. The success of the Chariots, combined with other [Allied] commando raids in North Africa and Europe, including the successful attack on Saint Nazaire in March 1942, led him to desire his own naval commando force, as related in his memoirs:

I expressed the wish that (in February 1943) Konteradmiral Heye should be released from his present duties and placed at my disposal. I wanted him to become, as I put it, ‘the Mountbatten of the German Navy’. In the British Navy Admiral Lord Louis Mountbatten had under him the commandos and the units and means for the execution of smaller, individual naval enterprises. Hitherto no such forces or means had existed in the German Navy. Among them were frogmen, as they were called […] the midget submarines, the one-man torpedoes, explosive motorboats and similar weapons, which, given the chance, could often at small cost in men and material score very considerable successes.

Thus the Kleinkampfverbände (K-Verbände) were born, although it would be a year before they were committed to action, by which time [the Third Reich] had been firmly pushed onto the defensive.

(Emphasis added. Click here for more.)

To benefit from [Imperial] experience in the field of midget naval weaponry, staff at OKM asked for details of the [Axis] two-man midget submarine, the Ko-Hyoteki, instructing the [Kriegsmarine] Attaché in Tōkyō, Konteradmiral Wenneker, to obtain the necessary information. On 3 April Wenneker in company with the [Regia Marina] Attaché were allowed to visit Kure where they inspected a Type A Ko-Hyoteki. This type had been involved in raids on Pearl Harbor, later also attacking Sydney Harbour and Diego Suarez.

Wenneker went to the meeting armed with forty-eight questions to which OKM desired responses, though many ultimately remained unanswered as the [Imperial] military, like that of [the Third Reich], guarded their technological secrets somewhat jealously. Wenneker reported his findings to Berlin, though nothing came of his despatch until much later in the year.

In actuality the original theoretical concept of the K-Verbände was more akin to the British Commando service than the naval organisation [that] it became. Though the German [anticommunists] were in the ideal position to learn from the experiences of their two major allies, [Fascist] Italy and [the Empire of] Japan, in their use of midget weapons, they failed to fully capitalise on this.

Quoting Spencer C. Tucker & alia’s World War II at Sea: An Encyclopedia, page 724:

A [Kriegsmarine] program, hoping to build on the success of the Maiale, was perhaps the most extensive yet least productive effort by the warring powers to build a midget submarine.

Quoting Erminio Bagnasco’s Italian Assault Craft, 1940–1945: Human Torpedoes and other Special Attack Weapons, page 51:

Three main ‘Kaiten’ models were built: the second, produced in very few units, was propelled by a closed-cycle turbine of the [Kriegsmarine] ‘Walter’ type, and could reach 40 knots.

The idea of using guided torpedoes crewed by pilots consciously devoted to sacrifice had been cherished for some time in [Imperial] naval circles, that had followed with interest and admiration the successes achieved in two world wars by the [Regia Marina] even if the [Regia Marina] did not expect the voluntary sacrifice of the operators.

We see numerous themes here: WWI’s influence on Fascism, the Regia Marina’s influence on foreign empires, geopolitics’ influence on military technology, and, of course, the importance of submarine warfare. Note also the economics: since human torpedoes are cheaper than battleships, and Fascist Italy had a sometimes wanting military budget, this made them attractive thereto in more ways than one.

See also: Frogmen First Battles