Scapa Flow (Old Norse: Skalpaflói) is a body of water in the Orkney Islands, Scotland, United Kingdom, sheltered by the islands of Mainland, Graemsay, Burray, South Ronaldsay and Hoy. At 360 km² with a sandy bottom and relatively shallow (not deeper than 50 metres and most of it about 20 metres deep), it is one of the great natural harbours/anchorages of the world, with sufficient space to hold a number of navies. Viking ships anchored in Scapa Flow more than 1000 years ago, but it is best known as the site of the United Kingdom's chief naval base during World War I and World War II. The base was closed in 1956.

World War I

Base for the British Grand Fleet

Historically, the main British naval bases were located near the English Channel to better face England's old enemies of France, Spain, and the Netherlands. In 1904, in response to the build-up of the German Kaiserliche Marine's High Seas Fleet, it was decided that a northern base was needed, to control the entrances to the North Sea. Originally, Rosyth was considered for the base, and then Invergordon at Cromarty Firth but construction in both places was delayed, leaving them largely unfortified by the time of the First World War. Scapa Flow was used many times for exercises in the years leading up to the War, and, when the time came for the fleet to move to a northern station, Scapa Flow was chosen for the main base of the British Grand Fleet, even though it was also unfortified.
John Rushworth Jellicoe, admiral of the Grand Fleet, was constantly nervous about potential submarine or destroyer attacks on Scapa Flow, and the base was reinforced with minefields, artillery, and concrete barriers starting in 1914. These fears were borne out when German U-boats twice attacked British ships in Scapa Flow, though the attacks themselves did no damage. The first, by U-18, took place in November 1914; but the sub was rammed by a trawler searching for submarines while it was trying to enter Scapa Flow, causing the submarine to flee and then sink. The second attack, by UB-116, in October 1918, encountered the sophisticated defences then in place at Scapa Flow, was detected by hydrophones and then destroyed by shore-triggered mines before it could enter the anchorage.

Scuttling of the German fleet

Following the German defeat in the First World War, 78 ships of the Kaiserliche Marine's High Seas Fleet were interned in Gutter Sound at Scapa Flow pending a decision on their future in the peace Treaty of Versailles. On 21 June 1919 Rear Admiral Ludwig von Reuter, the German officer in command at Scapa Flow, after waiting for the bulk of the British fleet to leave on exercises, gave the order to scuttle the ships to prevent their falling into British hands. Fifty-one ships sank without loss of life. However, nine German sailors died when British forces opened fire as they attempted to scuttle their ship, reputedly the last casualties of the First World War.

World War II

Early in World War II, on 14 October 1939, U-47, under the command of Günther Prien, penetrated Scapa Flow and sank the World War I-era battleship anchored in Scapa Bay. Her second torpedo attack blew a 30-foot (9 m) hole in the Royal Oak and as a result she flooded and quickly capsized. Of the 1,400-man crew, 833 were lost. The wreck is now a protected war grave. After the attack, Winston Churchill ordered the construction of a series of causeways to block the eastern approaches to Scapa Flow; they were built by Italian prisoners of war held in Orkney. These "Churchill Barriers" now provide road access from the Mainland to Burray and South Ronaldsay, although they block maritime traffic.

Three days after this submarine attack, four Luftwaffe Junkers Ju 88 bombers raided Scapa Flow in one of the first bombing attacks on Britain during the war. The attack badly damaged an old base ship, the battleship , with one bomber shot down by an anti-aircraft battery on Hoy.

Today

Usage by the petroleum industry

Scapa Flow is one of the petroleum refining and transfer points for North Sea oil. A 30-inch, 128-mile long underwater pipeline transports oil drilled from the Piper oilfield to the Flotta oil terminal. The Claymore and Tartan oil fields also feed into this line.

Scuba diving

The wreckage of the German fleet has become increasingly popular as a venue for recreational Scuba divers. Divers must first obtain a permit from the Island Harbour Authorities, which is available through diving shops and centres. The wrecks are mostly located at depths of 35 to 50 metres. Divers are permitted to enter inside the wrecks, but not to retrieve artefacts located within 100 metres of any wreck. However time and tide has washed broken pieces of ships' pottery and glass bottles into shallow waters and onto beaches. The underwater visibility, which can vary between 2 and 20 metres, is not sufficient to view all the length of most wrecks at once, however, current technology is now allowing 3D images of them to be seen.

The wrecks of the and the dreadnought , which exploded at anchor during the First World War, are war graves. Only divers of the British armed forces are permitted to visit them.

Scapa Flow Visitor Centre

The Scapa Flow visitor centre, at Lyness on the island of Hoy, is located in the former naval fuel pumping station and a converted storage tank. Exhibits include a large three dimensional representation of the island and of the ships as they were prior to scuttling. The island is accessible by local ferry several times daily from Houton. The centre has catering facilities for day trippers.

Gallery

See also

• Lamb Holm

• Glims Holm

• Scapa distillery