Neglected during World War II, the infrastructure in national parks continued to deteriorate as visitation soared afterward, leading to widespread complaints. In 1955 Congress funded an improvement program for completion by the NPS’s 50th anniversary in 1966. The use of modern materials and prefabricated components were encouraged to quickly and inexpensively construct low-maintenance buildings. This architectural style was a deliberate departure from the rustic buildings associated with national parks, which was considered outmoded and too labor-intensive for the needed scale of construction. Mission 66 revitalized many national parks; in Yellowstone, intended to be the program’s showpiece, its legacy includes some regrets.