SS Alcantara was an ocean liner that went into service just weeks before the start of World War I, was converted to an armed merchant cruiser in 1914, and was sunk by the German armed merchant cruiser SMS Greif on 29 February 1916 in the North Sea. Alcantara was built by Harland & Wolff for Royal Mail Lines, launched in October 1913 and made her maiden voyage in June 1914, following a Southampton-South America route. In 1915 the ship was armed with six 6-inch guns, anti-aircraft guns and depth charges, and commissioned as HMS Alcantara.