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World War II: wartime innovation and postwar reconstruction (1939–1945)

World War II (1939–1945) and its aftermath was a major factor in driving innovation in building technology, and in turn, architectural possibilities. The wartime industrial demands resulted in shortages of steel and other building materials, leading to the adoption of new materials, such as aluminum, The war and postwar period brought greatly expanded use of prefabricated building; largely for the military and government. The semi-circular metal Nissen hut of World War I was revived as the Quonset hut. The years immediately after the war saw the development of radical experimental houses, including the enameled-steel Lustron house (1947–1950), and Buckminster Fuller's experimental aluminum Dymaxion House.

The unprecedented destruction caused by the war was another factor in the rise of modern architecture. Large parts of major cities, from Berlin, Tokyo, and Dresden to Rotterdam and east London; all the port cities of France, particularly Le Havre, Brest, Marseille, Cherbourg had been destroyed by bombing. In the United States, little civilian construction had been done since the 1920s; housing was needed for millions of American soldiers returning from the war. The postwar housing shortages in Europe and the United States led to the design and construction of enormous government-financed housing projects, usually in run-down center of American cities, and in the suburbs of Paris and other European cities, where land was available,

One of the largest reconstruction projects was that of the city center of Le Havre, destroyed by the Germans and by Allied bombing in 1944; 133 hectares of buildings in the center were flattened, destroying 12,500 buildings and leaving 40,000 persons homeless. The architect Auguste Perret, a pioneer in the use of reinforced concrete and prefabricated materials, designed and built an entirely new center to the city, with apartment blocks, cultural, commercial, and government buildings. He restored historic monuments when possible, and built a new church, St. Joseph, with a lighthouse-like tower in the center to inspire hope. His rebuilt city was declared a UNESCO World Heritage site in 2005.