RMS Atrato was a passenger steamship launched on 22 September 1888 for the Royal Mail Steam Packet Company. She was renamed SS Viking in 1912 after her sale to the Viking Cruising Company. She was requisitioned by the Admiralty on the outbreak of the First World War and outfitted use as a naval auxiliary, being renamed again Viknor. She served alongside the 10th Cruiser Squadron under the Command of Commander E. O. Ballantyne with a complement of 22 officers and 273 ratings. She sank with the loss of all hands on 13 January 1915 while on active patrol duty in heavy seas off Tory Island. It is thought she struck a German naval mine.