RMS Alcantara was an ocean liner which entered service just weeks before the start of World War I, was converted to an armed merchant cruiser in 1915, and was sunk in combat with the German armed merchant cruiser in the Action of 29 February 1916.
Ocean liner
Harland and Wolff in Govan built Alcantara for the Royal Mail Steam Packet Company. She was one of the later members of RMSP's "A-series" of liners, which had begun with RMS Aragon launched in 1905. In common with all of the last four "A-series" ships, Alcantara had triple screws. A pair of four-cylinder triple-expansion steam engines drove the port and starboard pair. Exhaust steam from their low-pressure cylinders powered a Parsons low-pressure steam turbine that drove the middle screw propeller.
Alcantara was launched on 30 October 1913 and made her maiden voyage in June 1914 on RMSP's route from Southampton to Rio de Janeiro, Montevideo and Buenos Aires.
HMS Alcantara
In April 1915 the British Admiralty requisitioned Alcantara and her "A-series" sisters , and Andes to be armed merchant cruisers. She was armed with eight 6-inch guns, two six-pounder anti-aircraft guns, and depth charges. On 17 April at Liverpool she was commissioned into the Royal Navy's 10th Cruiser Squadron as HMS Alcantara, with the pennant number M 94. Arlanza and Andes were also commissioned into the 10th Cruiser Squadron, which joined the Northern Patrol that was part of the First World War Allied naval blockade of the Central Powers. The Squadron patrolled about of the North Sea, Norwegian Sea and Arctic Ocean to prevent German access to or from the North Atlantic.
German submarine attacks on ships voyaging to and from Arkhangelsk created a suspicion that the Imperial German Navy had established a submarine base somewhere in the Arctic. In the summer of 1915 Alcantara was sent to Jan Mayen Island to investigate. She arrived on 3 July and sent a landing party ashore. closed to 2,000 yards and slowed to lower a cutter to put an armed guard aboard the suspect ship.