A merchant submarine is a type of submarine intended for trade, and being without armaments, it is not considered a warship like most other types of submarines. The intended use would be blockade running, or to dive under Arctic ice.
Strictly speaking, only two submarines have so far been purpose-built for non-military merchant shipping use, though standard or partly converted military submarines have been used to transport smaller amounts of important cargo, especially during wartime, and large-scale proposals for modern merchant submarines have been produced by manufacturers.
Only two merchant submarines have historically been built, both in Germany during World War I. They were constructed to slip through the naval blockade of the Entente Powers, mainly enforced by the efforts of Great Britain's Royal Navy. The British blockade had led to great difficulties for German companies in acquiring those raw materials which were not found in quantity within the German sphere of influence, and thus was hindering the German war efforts substantially.
The submarines were built in 1916 by a private shipping company created for the enterprise, the Deutsche Ozean-Reederei, a subsidiary company of the North German Lloyd shipping company (now Hapag-Lloyd) and the Deutsche Bank. They were intended to travel the route from Germany to the neutral U.S., bringing back the required raw materials. As the U.S. would not profit enough from receiving German currency, the ships were to carry trade goods both ways.
Britain soon protested with the U.S. against the use of submarines as merchant ships, arguing that they could not be stopped and inspected for munitions in the same manner as other vessels. The U.S., under diplomatic pressure for supposedly showing favoritism while having declared itself neutral, rejected the argument. Even submarines, as long as they were unarmed, were to be regarded as merchant vessels and accordingly would be permitted to trade.
The Deutschland had a carrying capacity of 700 tons (much of it outside the pressure hull), and could travel at 15 knots (17.3 mph; 27.8 km/h) on the surface and 7 knots (8.1 mph; 13.0 km/h) while submerged. It had a crew of 29 men and was commanded by Paul König, a former surface merchantman captain.
On its first journey to the US, departing on the 23 June 1916, Deutschland carried 163 tons of highly sought-after chemical dyes, as well as medical drugs and mail. Passing undetected through the English Channel she arrived in Baltimore on the 8 July 1916 and soon re-embarked with 348 tons of rubber, 341 tons of nickel and 93 tons of tin, arriving back in Bremerhaven on 25 August 1916. She had travelled 8,450 nautical miles (9,724 mi; 15,649 km), though only 190 nmi (219 mi; 352 km) of these submerged.
The profit from the journey was 17.5 million Reichsmark, more than four times the building cost, mainly because of the high prices of the patented, highly concentrated dyes, which would have cost 26.9 thousand U.S. dollars per pound once adjusted for inflation. In return, the raw materials brought back covered the specific needs of the German war industry for several months.
A second journey in October-December of the same year was also very successful, again trading chemicals, medicines and gems for rubber, nickel, alloys and tin. However, the Deutschland was lightly damaged during a collision with a tug in New London. Following his return, captain Paul König wrote a book (or possibly had it ghost-written) about the journeys of the Deutschland. The book was heavily publicized, as it was intended to sway public opinion in both Germany and the U.S.
A third journey, planned for January 1917, was however aborted after the U.S. entered the war against Germany. The declaration of war had been partly because of U.S. anger over the actions of German submarines sinking shipping bound for Great Britain, sometimes just outside of American territorial waters (See SM U-53). The Deutschland was taken over by the German Imperial Navy and converted into the submarine cruiser (U-kreuzer) U-155 (a type of submarine with added artillery to fight when surfaced). It was successful in three war cruises, sinking 43 ships. After the war it was taken to England as a war trophy in December 1918. Scrapped in 1921, the boat's history ended on a tragic note, with 5 workers dying due to an explosion ripping apart the sub during dismantling.
A second merchant submarine, the sister ship of Deutschland, was launched on its first journey in August 1916 under Karl Schwartzkopf, but never arrived in the US. Its fate was never decisively uncovered, though she may have collided with the British armed merchant cruiser HMS Mantua south of Iceland, as was theorized after the war. There are also presumptions that she might have hit a mine off the Orkney Islands.
Six further merchant submarines were in the process of being built by the Deutsche Ozean-Reederei when the US entered the war in early 1917. The construction of the merchant submarines was subsequently halted or changed into submarine cruisers, similar to the fate of Deutschland.
In World War II, Germany used milk cow submarines to refuel its hunter u-boats in the Atlantic. As these boats were part of Kriegsmarine (Nazi Germany's navy), did carry light armaments (anti-aircraft guns), and never engaged in trade as such, they do not qualify as merchant submarines. However, they shared the large amounts of cargo space compared to normal submarines of their day.
Germany forcibly acquired five Italian 'merchant submarines' (again having defensive armament and thus not legally merchant ships, though having many of the appropriate characteristics) from a relatively extensive Italian program after the Italian armistice in September 1943. For details see 'Italy' below.
A 12-boat 'R'-class of 2100-ton submarines had been designed in Italy to carry approximately 600 tons of cargo with a surface speed of 13 knots (15.0 mph; 24.1 km/h) and submerged speed of 6 knots (6.9 mph; 11.1 km/h). A 63-man crew would operate a defensive armament of three 20 mm guns. Romolo and Remo were laid down in July 1942 at the Tosi Yard in Taranto with launch scheduled for March 1943. Ten large submarines built for combat service were also scheduled for conversion to merchant service after their designs had been found unsuitable for use against allied convoys. These were the 880-ton Archimede, the 940-ton Barbarigo, the 951-ton Comandante Cappellini, the 1030-ton Alpino Bagnolini and Reginaldo Giuliani, the 1036-ton Leonardo da Vinci and Luigi Torelli, the 1331-ton Enrico Tazzoli and Giuseppe Finzi, and the 1504-ton Ammaraglio Cagni.
Conversions were to be accomplished at Bordeaux, with armament limited to defensive machine-guns, while the conversion cargo capacity of 160 tons also reduced reserve buoyancy from 20–25% to 3.5–6%. Several French submarines captured at Bizerta were also scheduled for conversion, being the 974-ton Phoque, Requin, Espadon, and Dauphin.
The ships were used on an eastbound route from Bordeaux to Singapore (then in Japanese, thus Axis, hands) with cargoes of mercury, steel and aluminum bars, welding steel, bomb prototypes, 20 mm guns, blueprints for tanks and bombsights, and up to a dozen passengers. Return trip loadings were 110 to 155 tons of rubber, 44 to 70 tons of zinc, 5 tons of tungsten, 2 tons of quinine, 2 tons of opium, bamboo, rattan and passengers. Comandante Cappellini, Reginaldo Giuliani, and Enrico Tazzoli departed Bordeaux in May, 1943. The first two completed their voyages in July and August, but Enrico Tazzoli was destroyed by allied bombers in the Bay of Biscay. Barbarigo was similarly destroyed during a June departure, but Luigi Torrelli reached Singapore in August.
Following the Italian armistice in September, Giuseppe Finzi and Alpino Bagnolini were seized by Germany while undergoing conversion at Bordeaux, and designated UIT-21 and UIT-22, respectively. Reginaldo Giuliani, Commandante Cappellini, and Luigi Torelli were seized by the Japanese in the East Indies, given to Germany, and designated UIT-23, UIT-24 and UIT-25, respectively. UIT-22 departed Bordeaux for Sumatra in January 1944 and was destroyed by RAF 262 squadron Catalina bombers off South Africa in March. UIT-23 was sunk by the British submarine Tally-Ho in February. UIT-24 departed Sumatra for Bordeaux in February, but returned to Sumatra in March after its refuelling ship was sunk.
Of the other ships, Ammiraglio Cagni surrendered at South Africa, Archimede and Leonardo da Vinci were sunk before conversion to merchant service while Romolo, Remo and the French Phoque were sunk prior to loading. The remaining 'R'-class submarines were not completed and conversion work ceased on the remaining three French submarines.
The Soviet Union had plans to construct cargo submarines both during World War II and in the Cold War, but these plans were never carried out. These would not strictly count as merchant submarines, as they would have been at least lightly armed and used mainly for directly war-related duties, such as supplying troops or delivering military forces to their targets. However, in the post-Cold War period, Soviet designers also proposed purely peaceful applications.
World War II
In World War II, the Soviet Union used submarines (as well as other ships) to supply the besieged Crimean port of Sevastopol. The largest could transfer up to 95 tons of cargo, loading even the torpedo tubes with supplies. Around 4,000 tons were delivered by about 80 runs of 27 submarines, though Sevastopol still eventually fell.
Based on this experience, the Soviet Navy's high command initiated a transport submarine program. A first project (Project 605) envisaged a sub that would be basically a towed barge, connected to a standard sub. This idea was discarded due to difficulties with the towing. Later, a small cargo submarine design (Project 607) with a capacity of 250 to 300 tons of solid cargo and two folding cargo cranes was proposed. No weapons beyond two deck guns were envisaged, and the design borrowed many existing parts from the earlier VI and VI-bis submarine series to simplify construction. However, by 1943 the strategic situation had changed, and the plans were not executed.
The Soviet Union envisaged and almost realized various concepts for large cargo submarines during the 1950s and 1960s, though these would not have been counted as merchant ships, being envisaged as navy landing ships to transport troops. They would have been amongst the largest submarines of their day, had they been built.
Post Cold War
In the 1990s, the Malachite design bureau proposed plans for submarines capable of transporting petroleum or freight containers in or through Arctic regions. It was envisaged that these ships would dive under the polar ice cap to travel directly between European and Asian ports, and possibly northern Canada, with the designers noting that:
"Given equal cargo capacity, the efficiency of an underwater container ship is considerably higher, for example, than that of an icebreaker transport ship of the Norilsk type. The underwater tanker is competitive."
The tanker and container variants would follow the same design as standard military nuclear submarines, with the tanker variant carrying almost 30,000 tons of petroleum, to be loaded and discharged from surface or underwater terminals. The container carrier was to transport 912 standard (20-foot) freight containers, loaded within 30 hours through hatches, assisted by internal conveyance systems. However, these plans came to nothing in the hard financial straits following the Soviet Union’s dissolution later in the 1990s.
The ship of a concept of Submarine Freight Transportation System (SFTS) is a new system approach to idea of ‘Submarine Cargo Vessel'. This concept was suggested in 1997 by Vladimir Postnikov and present time it is considered as a sea part of Global Intelligent Transportation System concept.
Similar to the post-Cold War ideas of the Soviet Union, there have been some concept plans to use atomic-powered submarine oil tankers to exploit Arctic oilfields in Alaska and Siberia. General Dynamics had apparently approached German shipbuilders during the early 1980s about the possible construction of either a US$725 million nuclear-powered or a US$700 million methane-powered version of a liquefied natural gas (LNG) submarine tanker to carry LNG from the Arctic to North America and Europe.
Another (albeit black market) type of 'trade' usage is the known use of narco submarines or 'drug subs' by drug smugglers. In one case, a Colombian drug cartel was even interrupted before finishing the construction of a professional-grade, 30 m long, 200 tons carrying-capacity submarine apparently intended for the cocaine trade with the U.S. At the time of the police raid, the submarine was being constructed in segmented parts in a warehouse high in the Andes near Bogotá. However, most drug subs so far are not as sophisticated as professional merchant submarines would be, being mainly intended to run just under the surface, rather than deeply submerged.
- Amphibious assault submarine
- I-351-class submarine
- Submarine Cargo Vessel
- Defensively Equipped Merchant Ships
- Narco submarine
- German Submarine Deutschland's Atlantic Crossing (information & speech transcript via the 'FirstWorldWar.com' private website)
- See German version of this article at Handels-U-Boot (German). Some references not yet available in English.
- The Submarine "Deutschland" (from the 'ColorantsHistory.org' website. Accessed 2008-08-20.)
- Directed Readings on the U-Boat War - Blake, Sam; East Carolina University, April 2003.
- HMS Mantua Aux 1914-8-5 (datasheet on 'Clyde Warships', private shipbuilding history site)
- The U-151 Class, U-Kreuzer (from the 'SteelNavy.com' website)
- Warships of the World — Kafka, Roger & Pepperburg, Roy L.; Cornell Maritime Press, 1946.
- Axis Blockade Runners of World War II - Brice, Martin; Naval Institute Press, ISBN 0-87021-908-1, 1981.
- The First Soviet Giants - Polmar, Norman; book excerpts adapted for Undersea Warfare, Fall 2001, Issue 4, Volume 1
- Submarine Tanker Plans - New York Times, Thursday 19 November 1981