Human torpedoes or manned torpedoes are a type of diver propulsion vehicle on which the diver rides, generally in a seated position behind a fairing. They were used as secret naval weapons in World War II. The basic concept is still in use by many navies around the world.


An Israeli entry into the secret world of the mini-sub is pictured below.

Israeli SDV, 1967

A typical manned torpedo has a propeller, hydroplanes, a vertical rudder and a control panel with controls for its front rider. It usually allows for two riders who sit facing forwards. It has navigation aids such as a compass, and nowadays modern aids such as sonar and GPS positioning and modulated ultrasound communications gear. It may have an air (or other breathing gas) supply so its riders do not have to drain their own apparatus while they are riding it. In some the riders’ seats are enclosed; in others the seats are open at the sides as in sitting astride a horse. The seat design includes room for the riders’ swim fins (if used). There are flotation tanks (typically four: left fore, right fore, left aft, right aft), which can be flooded or blown empty to adjust buoyancy and attitude.

The concept of a tiny manned submarine carrying a bomb was developed and patented by a British naval officer in 1909, but was never used during the First World War. The Italian Navy experimented with a primitive tiny sub carrying two men and a limpet mine as early as 1918 and this craft did have some success. The first truly practical human torpedo was the Italian Maiale (nicknamed the “pig” because it was difficult to steer) used in the Second World War.

(above) Manned torpedo, called Maiale, at the Museo nazionale della scienza e della tecnologia Leonardo da Vinci of Milan.

Operationally, the Maiale torpedo was carried by another vessel (usually a conventional submarine), and launched near the target. Most manned torpedo operations were at night and during the new moon to cut down the risk of being seen. Attacks in 1940 were unsuccessful but in 1941, the Italian navy (Regia Marina) successfully forced the harbor of Alexandria and damaged the two British battleships HMS Queen Elizabeth and HMS Valiant, as well as the tanker Sagona. This feat encouraged the British to develop their own torpedo “chariots”.

The last Italian model, the SSB (for Siluro San Bartolomeo, “San Bartolomeo Torpedo”) was built with a partly enclosed cockpit, a more powerful motor and larger 300 kg (660 lb) warhead (up from the earlier SLC’s 220 and 250 kg (490 and 550 lb) warheads). Three units were made but not operationally used because Italy surrendered in 1943.

(above) The first British version of the concept was named the Chariot.

Two models were made; Mark I was 20 feet (6.1 m) long while Mark II was 30 feet (9.1 m) long, both suitable for carrying two men. Later versions were larger, starting with the original X-class submarine, a midget submarine, 51 feet (16 m) long, no longer truly a human torpedo but similar in concept. The X-Craft were capable of 6.5 knots (12.0 km/h) on the surface or 5.5 knots (10.2 km/h) submerged. They were designed to be towed to their intended area of operations by a full-size ‘mother’ submarine.


The US Navy captured Japanese manned torpedoes during the Second World War and the idea of riding a torpedo into a harbor never caught on. However, the notion of transporting combat swimmers UDT/SEALs from a mother submarine to a point of departure to the land or to deploy a mine or other stand-off weapon had some appeal.

This led to the development of not only the Mark VIII SEAL Delivery Vehicle (SDV), but to a drydock shelter (DDS) that would house the SDV until it was able to deploy.

Attaching a DDS to a submarine

The SEAL Delivery Vehicle (SDV) could also be hauled to the water in a trailer.

MK-8 SDV 1990

It also had a sled that it could ride behind a small surface combatant until it needed to be deployed.

As with a human torpedo, the SDV (Mk 7, Mk 8 and MK 9) was wet, which means that the duration of the mission was generally shorter than it would be in a mini-sub that had a crew in a dry compartment.

SDV training ops, Sea of Cortez

In the photo above, SEALs deploy a Mark VIII SDV from a DDS attached to the USS Cavalla.


The MK 9 SEAL Delivery Vehicle was armed with two torpedoes.


Enter the Advanced SEAL Delivery System. It’s a much larger craft, with a much larger independent range and it can carry a much larger swimmer payload. The ASDS does not need a complicated drydock shelter. It mounts directly to the hull of its mother submarine.

Advanced SEAL Delivery System
ASDS mounted on USS Charlotte – SSN 766

Most information surrounding the ASDS is classified.


  1. Combat Beneath The Sea, by Willy-Charles Brou, Library of Congress #57-10109, provides much information about this subject from early development to operations to progression of modifications, and the training of the divers. Included are first hand narratives from the operators and divers involved. Plus, there is the complete timelines of high profile operations such as the British attacks on the Tirpitiz. An interesting story there is several first hand accounts of captured Brit divers standing on the deck of the Tirpitiz while nervously looking at their watches. They knew when the charges they had set were to explode and they were successful in making a commotion which got the attention of senior officers. Their purpose was to try to relocate on the deck because they had been directly above the charges they had placed. They were successful in that effort and when the charges lit off the whole deck rose into the air six feet before settling into the mud.

    The U.S. Navy also used human torpedoes (not mini-subs) to clear passages through the reefs at various islands in the Pacific where assault landings were to be made. At Guam, not less than 620 underwater mines and obstacles were found and destroyed. Perhaps lesser known is human torpedoes were used in Borneo and Singapore by both the Brits and the U.S. to sink jap heavy cruisers.

    Also, U.S. divers in human torpedoes were used to clear the paths for the D-Day invasions. The 9th Armored Division attached to U.S. 3rd Army used human torpedoes to take out the railway bridge at Remagen. These operations were the beginning of the UDT teams.

    From the book, on October 22, 1935, two engineers at the Italian naval base at La Spezia, Mr. Tesei and Mr. Toschi presented their plans for a human torpedo to the base commander. The commander passed the plans to Admiral Cavagnari who approved continued research. By December a working model was demonstrated to Admiral Falangola.

    Maiale, or ‘seaswine’, was from a comment made by Tesei after losing control and abandoning the human torpedo which then sank: “The swine got away from me again!” The name stuck.

    I’d strongly urge to get the book if interested in this fascinating subject.

    • The South Korean SDV’s are essentially torpedoes that they ride, or they were the last time that I was at Squadron 56. They were always trying to get the US SEALs (as opposed to ROK SEALs) to ride them, but the spinning propellor behind you was somewhat unnerving. The problem with that sort of system (and they were all human torpedoes in the beginning) is that they are difficult to maneuver.

      The US MK-7 and MK-8 SDV’s were a departure from that. You are buttoned up in a wet sub Front compartment has two operators, rear compartment has four operators wedged in like sardines. But you’re navigating intertially so you don’t look out. You’re in the boat, not on it. Big difference. Thank you for the book suggestion.

    • The MK-8 is miserable and the MK-9 is horrible to use from a crew perspective. I didn’t go into details but it’s horrible. The ASDS was a HUGE departure from the wet sub norm.

    • As I mentioned to Old NFO (above) none of them are the least bit enjoyable to use. And the US Navy considered the ROK SDV’s to be death machines. I was offered a ride on one but declined. I can’t help but think that the ROK’s have adopted a better SDV in the intervening years. The last time I was there was in the mid 90’s.

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