[1] Cammerer was working as the Executive Secretary of the Fine Arts Commission in Washington, DC, which reviewed agency projects in the capital against design guidelines and aesthetic issues.

The U.S. National Park Service's first director, Stephen Mather, had encountered Cammerer at the commission and recognized his competence as executive secretary.

Cammerer served as Mather's right-hand man in Washington and acted for him in his frequent absences over the next decade.

[1] Under his leadership, the NPS tripled the number of areas served, increased visitations from two to 16 million, became involved with recreational area planning and management, began to survey and record historic sites and buildings outside the existing parks, and worked with Congress to pass the Historic Sites Act, as well as a law establishing the National Park Foundation.

Strained relations with Secretary of the Interior Harold L. Ickes impaired Cammerer's effectiveness and health; he stepped down in 1940 following a heart attack the previous year.