Island in the North Sea, one of the North Frisian Islands, 68 km/42 mi northwest of Cuxhaven; area 0.6 sq km/0.2 sq mi; population (2007 est) 1,330. It is administered by the state of Schleswig-Holstein, Germany. It was a British possession from 1807 to 1890, when it was ceded to Germany in exchange for Zanzibar. In both world wars it was used as a naval base. It has health resorts and fishing industries.
Physical Situated 48 km/30 mi from the nearest point on the German mainland, the island lies in the Heligoland Bight (German Helgolander Bucht), a bay in the North Sea. It comprises a rocky plateau, 1.3 km/0.8 mi long and less than 500 m/1,640 ft at its widest point. A sandbank, the Dunsen-Insel, lies off the east coast. On three sides the island rises perpendicularly from the sea, forming a grass-covered triangle called the Oberland.
World wars I and II Germany established fortifications on the island during World War I which were razed after the war in accordance with the Treaty of Versailles (1919). Hitler refortified Helgoland intensively with a labyrinth of underground workings (some 13 km/8 mi in extent). U-boat pens lay underneath the cliffs, and the power station was protected by a great concrete bunker below the cliff. The fortifications were destroyed by the British Royal Navy in 1947, and the island was used by the British Royal Air Force for bombing practice until it was returned to the Germans in 1952.