HMS Pathfinder was the lead ship of the Pathfinder class scout cruisers, and was the first ship ever to be sunk by a torpedo fired by submarine. She was built by Cammell Laird, Birkenhead, launched on 16 July 1904, and commissioned on 18 July 1905. She was originally to have been named HMS Fastnet, but was renamed prior to construction.
Pathfinder spent her early career with the Atlantic Fleet, Channel Fleet (1906) and then the Home Fleet (1907). At the start of the First World War she was part of the 8th Destroyer Flotilla, in the Firth of Forth.
Pathfinder was sunk off St. Abbs Head, Berwickshire, Scotland, on Saturday 5 September 1914 by the German U-21, commanded by Leutnant zur See Otto Hersing. Typical of the scout cruisers' poor endurance, she was so short of coal whilst on patrol that she could only manage a speed of 5 knots, making her an easy target. The ship was struck in a magazine, which exploded causing the ship to sink within minutes with the loss of 259 men. There were 11 survivors.