HMS Pathfinder was the lead ship of her class of two British scout cruisers, and was the first ship ever to be sunk by a self-propelled 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. During the beginning of World War I, the Pathfinder was sunk on 5 September 1914 by a German U-boat, the SM U-21.

The Pathfinder-class cruisers were a pair of scout cruisers built for the Royal Navy in the first decade of the 20th century. The sister ships spent much of the first decade of their careers in reserve. When the First World War began in August 1914 they were given coastal defence missions, Pathfinder on the coast of Scotland and Patrol on the coast of Yorkshire. The latter ship was badly damaged when the Germans bombarded Hartlepool in December. She spent the rest of the war in British waters. The ship was paid off in 1919 and sold for scrap the following year. Pathfinder was sunk by a German submarine shortly after the war began, the first sinking of a British warship during the war by a German submarine.