The Calgarian was taken over by the Admiralty in 1914 and assigned to the 9th Cruiser Squadron which was composed of three cruisers of the Royal Navy and five auxiliary cruisers. The prime duty of this squadron was the patrol of the mid-Atlantic.

On 1st March 1918, under command of Captain R A Newton RN, the ship was engaged in convoying 30 merchantmen off the north coast of Ireland. In addition to her convoy duty, she was carrying a number of naval ratings who were being transferred to other ships or were going on leave. The German Admiralty had just initiated an intensive submarine campaign between Ireland and Scotland, and the Calgarian was the first victim of this concentration, receiving four hits in succession from submarine torpedoes. She sank in a very short time taking with her 2 officers and 47 ratings.

The Calgarian was built by the Fairfield Co in 1914. There is no exact position where she sank but if the position 2 miles north of Rathlin is correct, she would be lying in quite deep water beyond the reach of the average sport diver.