Mini Submarines — From WWII Midget Subs to Modern Covert Craft

The most successful midget submarines of WWII. In Operation Source (September 1943), X-craft penetrated the heavily defended Kaafjord in Norway and placed explosive charges under the German battleship Tirpitz, putting it out of action for six months. X-craft also surveyed Normandy beaches before D-Day and guided the invasion fleet to their landing zones. Six VCs were awarded to X-craft crews.

Italy's Siluro a Lenta Corsa (Slow-Running Torpedo), nicknamed "Maiale" (Pig) by its operators, was a revolutionary concept. Two frogmen in diving suits rode the torpedo-shaped craft to enemy ships, detached the warhead, clamped it to the hull with magnets, set a timer, and escaped. In December 1941, three SLCs penetrated Alexandria harbor and sank the British battleships HMS Queen Elizabeth and HMS Valiant — temporarily shifting the Mediterranean balance of power.

Five Ko-hyoteki midget submarines participated in the attack on Pearl Harbor on December 7, 1941, launched from mother submarines. None achieved confirmed hits, and all five were lost. However, Ko-hyoteki achieved success later in the war — they damaged the British battleship HMS Ramillies in Madagascar and attacked shipping in Sydney Harbor, Australia. Over 100 were built during the war.

The Kaiten ("Return to Heaven") was a manned suicide torpedo — a modified Type 93 Long Lance torpedo with a cockpit for a human pilot. The pilot would guide the weapon directly into an enemy ship. Over 100 Kaiten missions were launched from submarines and surface ships. They sank the destroyer escort USS Underhill and the oiler USS Mississinewa, plus damaged several other vessels. Approximately 100 Kaiten pilots died in operations.

The most effective of Germany's late-war midget submarines. Unlike the disastrous Biber and Molch one-man submarines, the Seehund was a properly designed two-man boat with acceptable seakeeping and endurance. Operating from Dutch ports in 1944-45, Seehunds sank 8 ships and damaged 3 more while suffering relatively low losses (35 lost out of 285 deployed). They were nearly impossible to detect with contemporary sonar due to their tiny size.

The primary covert insertion vehicle of US Navy SEAL teams. This "wet" submersible means operators sit in flooded compartments wearing diving equipment. Launched from a Dry Deck Shelter (DDS) mounted on Virginia or Ohio-class submarines, the SDV carries a pilot, navigator, and four combat swimmers to their objective. Being replaced by the Dry Combat Submersible (DCS) which keeps operators dry.

Built by Lockheed Martin (originally MSubs Ltd design), the DCS is a quantum leap over the wet SDV. Operators travel in a dry, pressurized compartment, arriving at the objective fresh and combat-ready rather than cold and exhausted from hours in open water. Can carry 18 personnel or configure for cargo/equipment transport. Launched from a modified Dry Deck Shelter.

North Korea's most numerous submarine type, with approximately 40 in service. A 34-meter diesel-electric coastal submarine used for infiltration, mine laying, and intelligence gathering. In September 1996, a Sang-O ran aground on South Korean coast while inserting commandos, triggering a 49-day manhunt. North Korean special forces submarines remain a serious asymmetric threat to South Korea.

A small North Korean midget submarine believed responsible for the sinking of the South Korean corvette ROKS Cheonan in March 2010, killing 46 sailors. The Yono class can carry two heavyweight torpedoes or mines. An estimated 10+ are in service. The Cheonan sinking demonstrated that even primitive midget submarines remain lethal threats in littoral waters.

Iran's most numerous submarine class, with an estimated 23 in service. Based on North Korean Yono-class technology, the Ghadir operates in the shallow, confined waters of the Persian Gulf where larger submarines cannot easily maneuver. Armed with torpedoes and possibly mines, these boats could threaten commercial shipping and naval vessels in the strategic Strait of Hormuz.

Triton Submarines builds luxury personal submersibles for superyacht owners and research institutions. Models range from the 2-person Triton 1650/2 (500m depth) to the Triton 36000/2 Hadal Exploration System — capable of reaching the deepest point in the ocean at 11,000m. The 36000/2 was the vehicle used by Victor Vescovo to dive the Mariana Trench in 2019.

What is the difference between a mini submarine and a midget submarine?

The terms are often used interchangeably, but generally a midget submarine is under 150 tons displacement and carries a crew of 1-6, while a mini submarine can be up to 300 tons. Midget subs are typically military vessels designed for covert missions — harbor penetration, mine laying, special forces delivery. Mini submarines also include civilian research vessels and tourist subs. Both are distinct from full-size submarines which displace thousands of tons.

Were mini submarines effective in World War II?

Yes, remarkably so relative to their size and cost. British X-craft crippled the German battleship Tirpitz in a Norwegian fjord. Italian frogmen in SLC "human torpedoes" sank or damaged multiple Allied warships in harbors. Japanese Ko-hyoteki midget subs attacked Pearl Harbor and Sydney Harbor. German Seehund midget subs sank 8 ships in the final months of the war. Their effectiveness was disproportionate to their size.

What is a SEAL Delivery Vehicle (SDV)?

The SDV is a "wet" mini submarine used by US Navy SEALs. The crew sits in a flooded compartment wearing diving gear and breathing from the sub's air supply. The current Mk 8 Mod 1 can carry a pilot, navigator, and 4 SEAL passengers. SDVs are launched from a Dry Deck Shelter (DDS) mounted on the back of a full-size submarine. They allow SEALs to approach a target covertly while conserving energy and air.

Do drug cartels really use submarines?

Yes. Drug trafficking organizations, particularly Colombian cartels, have built over 200 semi-submersible and fully submersible vessels since the early 2000s. These "narco-subs" are typically 10-25 meters long, built in jungle workshops from fiberglass, and can carry 5-10 tons of cocaine worth $100-200 million. Some are true submarines that travel fully submerged. The US Coast Guard and Navy intercept them regularly, but many evade detection.

Can tourists ride in submarines?

Yes, tourist submarines operate in several locations worldwide including Hawaii, Barbados, Aruba, Grand Cayman, Maldives, and South Korea. Companies like Atlantis Submarines operate battery-powered vessels that carry 48-64 passengers to depths of 30-45 meters. These are fully certified by maritime authorities and have perfect safety records. Tickets typically cost $100-150 per person.

What modern navies operate midget submarines?

Several navies maintain midget submarine capabilities. North Korea operates the largest fleet (approximately 70 Sang-O and Yono-class boats). Iran has Ghadir-class and Al-Sabehat 15 midget subs. South Korea operates the Dolgorae-class. Pakistan, Colombia, and several Southeast Asian nations also operate small submarines. Special forces units in many countries use swimmer delivery vehicles (SDVs) for covert operations.