page_title: Heligoland
section_title: 20th century
hierarchical_section_title: Heligoland / History / 20th century
caption_attribution_description: Heligoland in 1919 (Digitally altered slightly to fix the corners of the image.)
context_page_description: Heligoland is a small archipelago in the North Sea. A part of the German state of Schleswig-Holstein since 1890, the islands were historically possessions of Denmark, then became the possessions of the United Kingdom from 1807 to 1890, and briefly managed as a war prize from 1945 to 1952.
  The islands are located in the Heligoland Bight in the southeastern corner of the North Sea and had a population of 1,127 at the end of 2016. They are the only German islands not in the vicinity of the mainland. They lie approximately 69 kilometres by sea from Cuxhaven at the mouth of the River Elbe. During a visit to the islands, August Heinrich Hoffmann von Fallersleben wrote the lyrics to "Deutschlandlied", which became the national anthem of Germany.
  In addition to German, the local population, who are ethnic Frisians, speak the Heligolandic dialect of the North Frisian language called Halunder. Heligoland used to be called Heyligeland, or "holy land", possibly due to the island's long association with the god Forseti.
context_section_description: Under the German Empire, the islands became a major naval base, and during the First World War the civilian population was evacuated to the mainland. The island was fortified with concrete gun emplacements along its cliffs similar to the Rock of Gibraltar. Island defences included 364 mounted guns including 142 42-centimetre (17 in) disappearing guns overlooking shipping channels defended with ten rows of naval mines. The first naval engagement of the war, the Battle of Heligoland Bight, was fought nearby in the first month of the war. The islanders returned in 1918, but during the Nazi era the naval base was reactivated. Lager Helgoland, the German labour camp on Alderney, was named after the island.
  Werner Heisenberg (1901–1976) first formulated the equation underlying his picture of quantum mechanics while on Heligoland in the 1920s. While a student of Arnold Sommerfeld at Munich in the early 1920s, Heisenberg first met the Danish physicist Niels Bohr. He and Bohr went for long hikes in the mountains and discussed the failure of existing theories to account for the new experimental results on the quantum structure of matter. Following these discussions, Heisenberg plunged into several months of intensive theoretical research but met with continual frustration. Finally, suffering from a severe attack of hay fever, he retreated to the treeless (and pollenless) island of Heligoland in the summer of 1925. There he conceived the basis of the quantum theory.
  In 1937, construction began on a major reclamation project (Project Hummerschere) intended to expand existing naval facilities and restore the island to its pre-1629 dimensions. The project was largely abandoned after the start of World War II and was never completed.
caption: Aerial photograph showing new fortifications in 1919.
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