Havmanden - class submarine ( 1911 ) The " Havmanden " class was a class of six submarine s built for the Royal Danish Navy from 1911 to 1914 . Also later known as the A class , the boats were designed by the Austro - Hungarian firm Whitehead & Co . of Fiume . The first three submarines were built by the company , while the remaining three were constructed under license in Copenhagen . The boats were just over long and their armament consisted of two bow torpedo tubes , later supplemented with an machine gun . The boats had a single shaft and were propelled by a Fiat or M . A . N . diesel engine on the surface and two electric motors while submerged . Although there was at least one close call for the class leader during World War I , none of the six boats was sunk in service . All six boats of the class remained active in the Royal Danish Navy from their time of construction until 1928 , when the first two boats were stricken . The remaining boats were all stricken by 1932 . The " Havmanden " class served as the basis for the Austro - Hungarian Navy ' s s built during World War I . Design and construction . After taking delivery of its first submarine — the problematic , built at La Spezia by Fiat - Laurenti in 1909 — the Royal Danish Navy looked for a submarine design that could be built in Denmark . In 1910 , the Navy contracted with Whitehead & Co . of Fiume for the class ' namesake boat , , to be built by Whitehead , and plans for a second , , to be built at the Copenhagen Navy Yard . In May 1911 , while the first two were still under construction , the Navy ordered two more boats from Whitehead , and , and plans for a final two , and . The " Havmanden " - class boats were submarines that displaced surfaced and submerged . The boats were long with a beam of and a draft of . For propulsion , they featured a single shaft , a single Fiat or M . A . N . diesel engine for surface running , and twin electric motors for submerged travel . The diesels of the Whitehead boats were rated at , while the Copenhagen boats were . The boats were equipped with two bow torpedo tubes of , but had no deck gun s . In 1917 , all were outfitted with a single machine gun . The complement of the boats as built was ten men , but was later increased to fourteen . In December 1911 , " Havmanden " became the first boat of the class to be launched , with " Havfruen " and " Thetis " following in 1912 . " Triton " and " Najaden " were launched in 1913 , while " Nymfen " , the final ship constructed , was launched in February 1914 . After the outbreak of World War I , the Austro - Hungarian Navy seized plans for the " Havmanden " boats from Whitehead & Co . and used them as the basis for its four s . Service careers . Initially " Havfruen " , " Havmanden " , and " Thetis " received pennant numbers of " H 1 " , " H 2 " , and " T 1 " , respectively , but were changed to " 2 " , " 3 " , and " 4 " in April 1913 . The other three submarines — " 2den April " ( the newly renamed " Triton " ) , " Najaden " , and " Nymfen " — received pennant numbers " 5 " , " 6 " , and " 7 " at the same time . Sources do not report when any of the " Havmanden " boats were commissioned , but all boats were active for neutral Denmark during World War I . " Havmanden " had a narrow escape in September 1914 when a British submarine mistook her for a German U - boat and launched an unsuccessful torpedo attack on her . Late in their careers , the class was identified as the A class and the pennant numbers of all the submarines were prefixed with an " A " , becoming " A - 2 " to " A - 7 " . None of the boats , however , ever displayed an " A " on their conning tower s . " Havmanden " and " Thetis " were the first two boats taken out of service when they were stricken in April 1928 . " Havfruen " was the last boat removed from service when she was stricken in May 1932 . Class members . There were six submarines that were members of the " Havmanden " or A class . " Havfruen " ( A 2 ) . The plans for " Havfruen " were purchased in 1910 and the boat was built at the Copenhagen Navy Yard . She was launched on 31 August 1912 . She initially received the pennant number of " H 1 " , but was assigned the number " 2 " in April 1913 . She was later designated " A 2 " when the class became known as the " A class " late in her career . " Havfruen " was the last ship of the class to be removed from service when she was stricken on 3 May 1932 . " Havmanden " ( A 3 ) . " Havmanden " was ordered in 1910 from Whitehead & Co . in Fiume . She was launched on 23 December 1911 . She initially received the pennant number of " H 2 " , but was assigned the number " 3 " in April 1913 . In September 1914 , " Havmanden " , displaying her pennant number of " 3 " on her conning tower , was mistaken for the German U - boat by the British submarine , but " Havmanden " escaped without damage when " E11 " s torpedo missed its mark . " Havmanden " was designated " A 3 " when the class became known as the " A class " later in her career . Along with " Thetis " , she was one of the first two boats of the class removed from service when stricken on 26 April 1928 . " Thetis " ( A 4 ) . " Thetis " was ordered in May 1911 from Whitehead & Co . in Fiume . She was launched on 19 June 1912 . She initially received the pennant number of " T 1 " , but was assigned the number " 4 " in April 1913 . " Thetis " was designated " A 4 " when the class became known as the " A class " later in her career . She and " Havmanden " were stricken on 26 April 1928 , the first two boats of the class to be removed from service . " 2den April " ( A 5 ) . " Triton " was ordered in May 1911 from Whitehead & Co . in Fiume . She was launched on 31 March 1913 . Her purchase was financed by a subscription offer made by the public and , as a result , she had been renamed " 2den April " — in honor of the first Battle of Copenhagen , fought on 2 April 1801 — by the time she was assigned the pennant number " 5 " in April 1913 . She was designated " A 5 " when the class became known as the " A class " later in her career . After " 2den April " was stricken on 15 January 1929 , she was used as a target and ultimately broken up in 1932 . " Najaden " ( A 6 ) . The plans for " Najaden " were purchased in May 1911 and the boat was built at the Copenhagen Navy Yard . She was launched on 9 July 1913 . She was assigned the pennant number of " 6 " in April 1913 . She was designated " A 6 " when the class became known as the " A class " later in her career and was stricken on 9 September 1931 . " Nymfen " ( A 7 ) . The plans for " Nymfen " were purchased in May 1911 and the boat was built at the Copenhagen Navy Yard . She was launched on 10 February 1914 , and was the final ship of the class launched . She was assigned the pennant number of " 7 " in April 1913 , but designated " A 7 " when the class became known as the " A class " later in her career . " Nymfen " was stricken on 11 March 1932 .