Series 3: Correspondence, (1936-1954), is arranged alphabetically with the items within each folder arranged in reverse chronological order. It consists of correspondence exchanged between Earle and various individuals in the military, the federal government, academia, business, and University publishing. There are general alphabetical files, as well as separate folders for individuals with whom Earle had substantial correspondence. Prominent correspondents include: Herring Pendleton (President, Social Science Research Council and Assoc. Executive, Carnegie Corp. -- 1947-1948), Jacob Viner (Department of Economics, University of Chicago, -- 1944-1945), Sir John Slessor (Chief Air Marshall, R.A.F.-- -1948-1951), and William S. Culbertson (Chief, Geopolitical Section, MIS [Military Intelligence] -- 1942-1943).

Series 4: Professional Activities, (1937-1954) is arranged alphabetically within six subseries: The Princeton Military Studies Group, Government Consultant/Advisor, Professional Associations (other than ACIS), Professional-Related Activities, Conferences, and Interviews. The series consists primarily of correspondence, with some government reports, committee minutes, and news clippings interfiled. The Princeton Military Studies Group subseries reflects the activities of a group of scholars established by Earle to study broad questions of national strategy, military security, elements of military and economic power, and the role of the United States in world politics. The Government Consultant/Advisor subseries illustrates Earle's extensive work with federal government offices during World War II (especially with the Army Air Forces, Headquarters). Within the Professional Associations subseries, there is a substantial amount of material on Earle's involvement in the Council on Foreign Relations [CFR]. Aside from a number of general CFR folders, there are folders containing reports and correspondence of various CFR study groups, most substantially the Study Group on Anglo-American Relations (1952). The drafts of this study group's report are listed in the box listing. This subseries also contains a substantial amount of material on Earle's role as a trustee of the Foundation for the Advancement of the Social Sciences (based at the University of Denver). The Professional-Related Activities subseries highlights Earle's part in instigating citizen involvement in the War Effort and in several government projects. Information regarding a number of military policy conferences with which Earle was involved are contained in the Conferences subseries. The Interviews subseries contains dictations of interviews conducted by Earle with individuals such as Charles Dollard and Frederick Keppel of the Carnegie Corporation and Joseph H. Willets of the Rockefeller Foundation.