Helgoland (hĕlˈgōläntˌ) [key] or Heligoland hĕlˈĭgōlăndˌ, island (1994 pop. 1,730), c.150 acres (60 hectares), Schleswig-Holstein, NW Germany, in the North Sea. Formed of red sandstone, it rises to c.200 ft (60 m) above the sea and is largely covered with grazing land. Strategically located near the mouths of the Weser and the Elbe rivers, Helgoland was captured by the Danes in 1714, was occupied by the English in 1807, and was formally ceded to England by Denmark in 1814. In exchange for rights in Africa, England gave the island to Germany in 1890. The Germans installed fortifications, which were razed after World War I according to the terms of the Treaty of Versailles. However, Germany refortified Helgoland in 1936 and used it as a naval base in World War II. In 1947, British occupation authorities, after evacuating the islanders (mostly fishermen), blew up the fortifications and part of the island in one of the largest known nonatomic blasts. The island was largely rebuilt after British occupation forces returned it to West Germany in 1952. It is now a popular tourist resort and a center for scientific research, particularly ornithology.