Here's a photo looking east across Washington, D.C., in 1962. Look at all the temporary office buildings on the National Mall and in West Potomac Park!!
"Tempos" were first built on the Mall during World War I in order to provide office space for the Department of War. On the north side of the Mall between 17th and 21st Street were two buildings. Each was shaped like a comb, with the closed end against Constitution Avenue. This permitted natural light between each wing, and for multiple entrances in each courtyard (to ensure proper employee flow). The nine-wing Main Navy Building was to the east, and the eight-wing Munitions Building to the west. A parking lot existed between the buildings and the Reflecting Pool. These buildings, which were three stories tall, were massive, providing 1.8 million square feet of office space for 14,000 workers.
There were other tempos, too. Where the National Museum of the American Indian now stands (Jefferson Drive SW, 3rd Street SW, Maryland Avenue SW, Independence Avenue SW, 4th Street SW) was a seven-wing tempo. A four- or five-wing tempo stood at Jefferson Drive SW, 4th Street SW, 6th Street SW, jutting about a third of the way into the National Mall. A six-wing tempo stood where the east wing of the Air & Space Museum is now (Jefferson Drive SW, 4th Street SW, 6th Street SW, and Independence Avenue SW), and a five-wing tempo stood where the west wing of the Air & Space Museum is now (Jefferson Drive SW, 6th Street SW, 7th Street SW, and Independence Avenue SW).
Another structure was the Liberty Loan Building, an L-shaped, three-story structure adjacent to the south side of the Bureau of Printing and Engraving. Intended to house 1,200 workers, a whopping 1,800 employees jammed into its 93,000 square feet. (Two more stories were added in 1927.) The Liberty Loan Building is the sole surviving World War I temporary building.
All but the Main Navy Building and the Munitions Building had been torn down by 1937. But in early 1942 at the start of World War II, tempos were re-erected on all these sites as well as on the south side of the National Mall next to the Reflecting Pool and in West Potomac Park (where the MLK Memorial and FDR Memorial are today).
Most of the tempos lasted into the 1960s! The Navy and Munitions buildings did not come down until 1974.