Armed merchantman Armed merchantman is a term that has come to mean a merchant ship equipped with guns , usually for defensive purposes , either by design or after the fact . In the days of sail , piracy and privateer s , 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 able to defeat regular warships in battle ( see Battle of Pulo Aura ) . In more modern times , auxiliary cruisers were used offensively to disrupt trade chiefly during both World War I and World War II , particularly by Germany . 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 heavily armed in order to defend themselves against pirates and privateer s . They also defended themselves against warships , scoring signal victories at the Battle of Pulo Aura and the Action of 4 August 1800 . The British Royal Navy purchased several that it converted to ships of the line . Development of auxiliary cruisers . In 1856 , privateering ( or seizure of a belligerent country ' s merchant ships as a private enterprise ) lost international sanction under the Declaration of Paris . From 1861 - 65 European countries built high speed ships to run the Union Blockade during the American Civil War . Some of these were armed and served as Confederate States Navy raiders . Russia purchased three ships in 1877 of armed with guns for use as auxiliary cruisers for a " Russian Volunteer Fleet " . Germany and the United Kingdom responded to the precedent by asking their shipping companies to design fast steamers with provision for mounting guns in time of war . Russia built two more auxiliary cruisers in 1892 . In 1895 the Imperial German Navy mobilized the provisional auxiliary cruiser " Normannia " for a 15 - day trial armed with eight 6 - inch guns , two guns , six guns , and two torpedo boats . 20th century . In both World Wars both Germany and the United Kingdom used auxiliary cruisers . . Whilst the British used armed passenger liners defensively for protecting their shipping , the German approach was to use them offensively to attack enemy shipping . Armed merchant cruisers . The Armed Merchant Cruisers ( AMC ) of the British Royal Navy were employed for convoy protection against enemy warships . They had limited value because they lacked warship armour and used local control of guns rather than director fire - control system s . Many were later converted into troopships . One famous AMC of World War I was the British which , after a heated battle that caused heavy damage on both sides , succeeded in sinking the German auxiliary cruiser near the Brazilian island of Trinidade in 1914 . By coincidence , " Cap Trafalgar " was disguised as " Carmania " . In World War II , — the sole escort for convoy HX 84 in November 1940 — stood off the pocket battleship , when the German ship attacked the convoy . Though she was sunk , this enabled the convoy to escape . Her master , Acting Captain Edward Fegen was awarded the Victoria Cross ( posthumous ) for his actions . Another famous action involving an armed merchant cruiser was the November 1939 battle between and the German battlecruisers and . Fighting against hopeless odds , the " Rawalpindi " was quickly sunk . Auxiliary cruisers . Both the Spanish and United States Navy used auxiliary cruisers during the Spanish - American War of 1898 . In World War I too , American auxiliary cruisers fought several engagements with German U - boats . 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 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 . was a former passenger liner that sank two freighters in 1914 before being caught by . Her sister ship , , 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 the Americans interned her and eventually converted her into the United States Navy troop transport USS " Von Steuben " . The most famous German commerce raider of World War I probably was , a sailing ship under the command of the legendary Count Felix von Luckner . However , both and were each much more successful than " Seeadler " . 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 : To preserve their cover , these ships flew the flags of neutral or occasionally Allied nations . They re - fuelled and provisioned themselves from special supply ships , from Japanese island bases , or simply 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 . In one incident , the German ( ex - merchantman " Steiermark " ) managed to surprise and sink the Australian light cruiser , which approached too close , though " 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 . It should be noted that " Kormoran " s attack upon " Sydney " was motivated by desperation . However , she was not the most successful German raider of World War II ( both and scored higher kill tonnages ) . Another , , was also sunk in a mutually destructive engagement with the American Liberty Ship . The only encounters between Allied and Axis auxiliary cruisers in World War II were all with the raider . This small vessel , which captured or sank 22 merchantmen , encountered three British AMCs in her career , defeating HMS " Alcantara " and HMS " Carnarvon Castle " and later sinking HMS " Voltaire " . During World War II , German auxiliary cruisers are believed to have either sunk or captured some of Allied shipping . Compare to the Q - ship , which was a disguised merchantman for anti - submarine operations . Others . 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 . Russo - Japanese War . Russian merchant cruisers . Note : This listing is incomplete . Spanish Civil War . The Spanish Nationalist s , whose navy was substantially outnumbered by the Republicans , made an extensive use of auxiliary cruisers during the Spanish civil war , two of them on loan 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 . The armament varied but six guns with guns as secondary was usual . From 1941 , many served as troopships . French Navy ( " Marine Nationale " ) . French auxiliary cruisers were armed with 138 mm , 152 mm or 150 mm guns , 75 mm 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 offensive 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 . Armament usually consisted of six 6 in guns , two to six torpedo tube s , and an assortment of , 37 mm , and automatic weapons . Most of these merchant raider s carried an Arado Ar 196 floatplane for reconnaissance . , , and were also equipped with small motor torpedo boat s . 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 " ) were deployed to destroy or capture Allied merchant ships . All of them mounted two guns . 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 hose s to repel boarders . One exception to this are the ships of Pacific Nuclear Transport Limited , which are used to transport spent nuclear fuel and reprocessed uranium on behalf of BNFL . Transporting enough fissile material between them to produce 50 - 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 or three autocannon s . In April 2010 , it was reported that a Russian company is offering a version of the 3M - 54 Klub missile that can be disguised and launched from a shipping container , in theory enabling any cargo ship to be armed with an anti - ship missile . This type of missile is allegedly capable of disabling or even sinking an aircraft carrier . During the 2011 Libyan civil war , forces loyal to Gaddafi armed several merchant vessels and attempted to use them to blockade the port of Misrata . In October 2011 , the British Prime Minister , David Cameron , announced that British merchant shipping passing through areas known for piracy , could carry firearms .