HMS Sentinel was one of two Sentinel-class scout cruisers built for the Royal Navy in the first decade of the 20th century. The ship was initially assigned to the Mediterranean Fleet before returning home and being reduced to reserve in 1907. Recommissioned two years later as part of the Home Fleet, she spent the next five years moving on and off of active service in British waters. Sentinel was assigned to coastal defence duties when the First World War began in 1914, although she was transferred to the Mediterranean in 1915. By 1918 the ship had been assigned to the Aegean. After the end of the war in November, Sentinel was sent to the Black Sea as the British attempted to intervene in the Russian Civil War. The ship returned home in early 1919 and was paid off. She became a training sh