SS Calgarian was an Allan Line steam turbine ocean liner that was built in 1914 and converted into a Royal Navy armed merchant cruiser.

Until 1916 she served with the 9th Cruiser Squadron, patrolling off West Africa and then off the east coast of the United States.

An Imperial German Navy U-boat sank her off Rathlin Island, Ireland on 1 March 1918.

The Fairfield Shipbuilding and Engineering Company built Calgarian at Govan, Glasgow for the Allan Line's primary service between Liverpool, England and the Canadian ports of Quebec and Montreal.

Each shaft drove a four-bladed bronze propeller for a designed sea speed of 19 knots.

She then crossed the North Atlantic, and from 20 March until 12 June 1915 she was based at Halifax, Nova Scotia on the North America and West Indies Station (with its headquarters and Royal Naval Dockyard at the Imperial fortress colony of Bermuda).

She then returned via St John's, Newfoundland and Gibraltar carrying Canadian troops to Liverpool, where she arrived on 10 July 1915.

She left two days later and reached Devonport, England on 20 October, where her logbook records that "HRH disembarked".

[5] For the remainder of the war, Calgarian made transatlantic voyages, mostly between Liverpool and Halifax.

[5] In July 1917 Canadian Pacific bought Allan Line, including Calgarian,[6] but she remained in Royal Navy service.

However, the hawser broke, and Calgarian sank north of Rathlin Island with the loss of 49 men.