SS Cap Trafalgar was a German ocean liner launched in 1913 for the Hamburg Süd line. In 1914, she was converted for use as an auxiliary cruiser during World War I. She was the first armed merchant cruiser sunk by a ship of the same class; she was destroyed by HMS Carmania, also a converted ocean liner, in a furious action in the South Atlantic on 14 September 1914. It was the world's first battle between former ocean liners.
SMS Cap Trafalgar
Carmania sinking Cap Trafalgar
Cap Trafalgar and Eber in Trindade
The Carmania
An armed merchantman is a merchant ship 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.
HMS Alcantara and SMS Greif dueling at close range during the action of 29 February 1916
RMS Carmania sinking SMS Cap Trafalgar near the Brazilian islands of Trindade, 14 September 1914
Kormoran in 1940. During a single ship action on 19 November 1941, off the coast of Western Australia the German auxiliary cruiser Kormoran sank HMAS Sydney before being scuttled.