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.