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Armed merchantmen

Armed Merchantmen has come to mean merchant ships equipped with guns, usually for defensive purposes, either by design or after the fact. In the days of sail, piracy and privateers, many merchantmen would be routinely armed, especially those engaging in long distance and high value trade. The most famous of this type were the East Indiamen which were known to be able to defeat regular warships in battle.

Pre-20th century

East Indiamen of various European countries were heavily armed for their long journeys to the Far East. In particularly dangerous times, such as when the home countries were at war, a convoy system would be used whereby the ships were escorted by a warship. However, many East Indiamen also travelled on their own, and therefore were armed to the same standard as a ship of the line in order to defend themselves against pirates and privateers.

Development of Auxiliary Cruisers

  • 1856 - Privateering (or seizure of a belligerent country's merchant ships as a private enterprise) lost international sanction under the Declaration of Paris.
  • 1861-65 - Europe built high speed ships to run the American Civil War Union Blockade. Some were armed and served as Confederate States Navy raiders.
  • 1877 - Russia purchases three ships of 6000 tons armed with 15 cm (6-inch) guns for use as auxiliary cruisers for a Russian Volunteer Fleet. Germany and the United Kingdom respond to the precedent by asking their shipping companies to design their fast steamers with provision for mounting guns in time of war.
  • 1890 - German and British shipyards have built new civilian ships designed for wartime conversion, and France, Italy, Japan, Austria-Hungary, and the United States have made similar agreements with their shipyards.
  • 1892 - Russia builds two more auxiliary cruisers.
  • 1895 - The Imperial German Navy mobilizes the provisional auxiliary cruiser Normannia for a 15 day trial armed with 8x15-cm guns, 2x9-cm guns, 6x37-mm guns, and 2 torpedo boats.

20th century

These were used in both World Wars by both Germany and the United Kingdom. Whilst the British used armed passenger liners for protecting their shipping, the German approach was to use them to attack enemy shipping.

Armed merchant cruisers

The Armed Merchant Cruisers (AMC) of the British Navy were employed for convoy protection against enemy warships. They were found to be of limited usefulness because they lacked warship armour and used local control of guns rather than director fire-control systems. Many were converted into troopships.

One famous AMC of World War I was the British RMS Carmania which, after a heated battle which caused heavy damage on both sides, succeeding in sinking the German auxiliary cruiser Cap Trafalgar near the Brazilian island of Trinidade in 1914.

In World War II, the Jervis Bay, the sole escort for convoy HX 84, stood off the pocket battleship Admiral Scheer, when the German ship attacked the convoy. Though she was sunk, this enabled the convoy to escape. Her master, Acting Captain Edward Fegan was awarded the Victoria Cross (posthumous) for his actions.

Auxiliary cruiser

The German practice was to arm merchantmen with hidden weapons and use them as commerce raiders. An auxiliary cruiser - Hilfskreuzer or Handels-Stör-Kreuzer (HSK) - usually approached her target under a false flag with guns concealed, and sometimes with her appearance altered with fake funnels and masts and often a fake paint job. The victim was thus engaged at point-blank range and had no chance to escape. In World War I, the Imperial German Navy initially used fast passenger ships (such as past holders of the Blue Riband for fastest North Atlantic crossings), but they made obvious and easy targets because of their very familiar silhouettes. The Germans therefore soon moved on to using captured and refitted Allied vessels, but principally only modified transport ships. These were slower, but less recognizable. In both world wars, these ships were found to be vulnerable to attack, and were withdrawn before the war ended. Many were sunk after being caught by regular warships - an unequal battle since auxiliary cruisers had poor fire control and no armor. There were, however, a few success stories. The Kaiser Wilhelm der Große was a former passenger liner that sank two freighters in 1914 before being caught by HMS Highflyer. Her sister ship, the Kronprinz Wilhelm, had a legendary journey, sinking or capturing a total of 15 ships in 1914 and 1915, before finally running out of supplies and having to put into port in Virginia, where she was interned by the Americans and eventually converted into a US Navy troop transport (as the renamed USS Von Steuben). The most famous German commerce raider of WWI probably was SMS Seeadler, a sailing ship commanded by the legendary Count Luckner.

The concept was revived in the Second World War. In one incident, the German Kormoran (ex-merchantman Steiermark) managed to surprise and sink the Australian light cruiser HMAS Sydney, which approached too close, though the Kormoran herself was also sunk in the engagement. This was the only occasion in history when an armed merchantman managed to sink a modern warship; in most cases auxiliary cruiser raiders tried to avoid confrontation with warships.

In World War II, the German Navy operated ten very successful auxiliary cruisers which ranged in tonnage from 3,860 - 9,400; typically these vessels were equipped with:

  • Floatplanes
  • 15 cm guns
  • Smaller armaments (typically hidden away behind specially designed and hinged bulwarks, or beneath fake deckhouses and/or skylights)
  • Torpedoes
  • Mines

To preserve their cover, these ships flew the flags of neutral or occasionally Allied nations. They were re-fuelled and provisioned by special supply ships and from Japanese island bases, or they simply reprovisioned themselves from prizes they had taken.

To counter the effectiveness of these disguises the Allies introduced the check-mate system in 1942 to identify individual ships on a one-by-one basis with the Admiralty in London.

During World War II German auxiliary cruisers are believed to have either sunk or captured some 800,000 tons of Allied shipping.

Compare to the Q-ship, which was a disguised merchantman for anti-submarine operations.


The CAM Ship (from catapult armed merchantman) was a British merchantman fitted with a catapult that could launch, but not recover, a single fighter aircraft.

The Merchant Aircraft Carrier or MAC was a British or Dutch cargo ship with a flight deck that could carry a small number of aircraft.

CAM and MAC ships remained as civilian ships operated by civilian crews, with Fleet Air Arm or Royal Netherlands Navy "air parties".

Ship lists

Spanish-American War

American auxiliary cruisers

Russo-Japanese War

Japanese merchant cruisers Russian merchant cruisers Note: This listing is incomplete.

World War I

Allied merchant cruisers

Royal Navy French Navy

German auxiliary cruisers

Spanish Civil War

The Spanish Nationalist, whose navy was substantially outnumbered by the Republicans, made an extensive use of auxiliary cruisers during the Spanish civil war, two of them lend from Italy:

World War II

Allied merchant cruisers

The Armed merchant cruisers were made by requisitioning large ships and providing them with guns and other equipment. They ranged from 6,000 tons to 22,000 tons. The armament varied but six guns with guns as secondary was usual. From 1941 many served as troopships. Royal Australian Navy

French Navy (Marine Nationale) French auxiliary cruisers were armed with 138 mm, 152 mm or 150 mm guns, 75 and 37 mm AA guns and 13.2 mm or 8 mm AA HMG

German auxiliary cruiser raiders

At the outbreak of war, the German Navy (Kriegsmarine) requisitioned a number of fast merchantmen and immediately sent them into naval shipyards to be converted into auxiliary cruisers. These ships had at the time of building been fitted with extra strong decks specifically to facilitate the installation of military equipment when required, but this was the only difference between them and other merchantmen of the period. No precise plans had been drawn up for the conversion of these ships into warships, and consequently the conversion process was painfully long. Compared to the diversity of British auxiliary cruisers, the Hilfskreuzer were standardized insofar as possible. The ships themselves averaged approximately 7,000 tons. Armament usually consisted of six 15 cm (5.9-inch) guns, between two and six torpedo tubes, and an assortment of 40 mm, 37 mm, and 20 mm automatic weapons. Most of these merchant raiders carried an Arado Ar-196 seaplane for reconnaissance. Kormoran, Komet, and Michel were also equipped with small motor torpedo boats. In addition to armament, increased fuel, water, and coal storage had to be provided for as well. Furthermore, the raiders could not abandon the crews of their captures, so space had to be provided for prisoners. The first Hilfskreuzer got under way in March 1940, shortly before the Norwegian campaign.

Japanese armed merchant cruisers

See also Japanese raiders in Indian Ocean Campaign and List of Japanese Auxiliary Cruiser Commerce Raiders.

Japan converted fourteen merchant ships to "armed merchant cruisers." But, by the end of 1943, five had been sunk and seven had been converted back to merchant ships.

Italian armed merchant cruisers

Unlike the Germans and the Japanese, none of the armed merchant cruisers (or auxiliary cruisers) of the Italian Royal Navy (Regia Marina Italia) were deployed to destroy or capture Allied merchant ships.

  • Ramb I - Lost on 27 February 1941
  • Ramb II - Never active as an Italian armed merchant cruiser and, after being chartered by the Japanese as the Calitea II, lost on 12 January 1945
  • Ramb III - Converted into an escort vessel and never served as an armed merchant cruiser
  • Ramb IV - Converted into a hospital ship and never served as an armed merchant cruiser

21st century

Despite a rise in modern piracy it is very unusual for modern merchant ships to be armed, save for maybe a number of small arms and the use of the ship's fire hoses to repel boarders. One exception to this are the ships of PNTL used to transport spent nuclear fuel and reprocessed uranium on behalf of BNFL. Transporting enough fissile material between them to produce 50 to 60 nuclear weapons these ships, beginning with the Pacific Pintail and Pacific Teal, became armed in 1999 to avoid the cost of a Royal Navy escort, . Travelling together in convoy during these ships intermittent voyages they have an onboard escort of armed police from the UKAEAC and its successors and are equipped with two to three automatic cannon of 30mm calibre.

See also


  • Duffy, James P., Hitler's Secret Pirate Fleet, 2001, Praeger, Westport (Connecticut) and London, ISBN 0-275-96685-2
  • The Oxford Companion to World War II (2005) ISBN -X
  • Alfred von Niezychowski, The Cruise of the Kronprinz Wilhelm, 1928, published by Doubleday

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