After the Imperial War Museum was formally established by an act of Parliament in 1920, the museum operated in the Crystal Palace. From 1924 to 1935, it operated from two small galleries adjoining the Imperial Institute. It reopened in 1937 in the former Bethlem Royal Hospital on Lamberth Road, Southwark, which continues to be the main branch of the museum.
The museum has permanent displays open to the public. In addition, it has vast archives which are accessible by appointment. Collections include documents, works of art, firearms, photographs, and printed books.