Scapa Flow is a body of water in the Orkney Islands, Scotland, United Kingdom. Surrounded by the islands Mainland, Graemsay, Burray, South Ronaldsay and Hoy, it is best known as the United Kingdom's chief naval base during the First and Second World War. Following the German defeat in the First World War, the German fleet was held in Scapa Flow until the admiral scuttled the ships to prevent them falling into British hands. The wrecks are still in Scapa Flow, and are a popular target for divers.
Already used by war ships in the Viking era, the base remained in use by the British navy until 1956. During both World Wars, German submarines have succeeded in sinking British ships.
In Cockney rhyming slang, the word Scarper, meaning to run away, derives from Scapa Flow rhyming with "go".