The U.S. government constructed a number of temporary buildings on the National Mall during World War I and II which stood from 1918 until 1971. They were built due to the urgent need for office space during wartime, but they remained in use during peacetime even though they disrupted the intended layout of the mall according to the McMillan Plan for over half a century.
In 1918, the Main Navy and Munitions Buildings were constructed alongside the Lincoln Memorial Reflecting Pool in West Potomac Park, and a cluster of six buildings was built in the center of the Mall in the vicinity of 7th Street. All but one of the latter six buildings was demolished by 1937. However, fourteen new temporary buildings were constructed throughout the Mall in 1942. Most of these stood until the mid-1960s, and the last one was demolished in 1971. Constitution Gardens, the National Museum of American History, National Gallery of Art, and National Air and Space Museum were all built at the locations of demolished temporary buildings.