The collection contains newspapers, periodicals, correspondence, maps, military documents, including declassified items, and a variety of publications - government, military and other - relating to the Pacific Theater during World War II, specifically the Japanese occupation of the Philippines, the establishment of the Commonwealth of the Philippines and the American return to the Philippines, the American occupation of Japan and Korea, the Japanese war crime trials and the post-war economies of the Philippine Islands, Japan and Korea. Of particular note is Simpson's 161-page documentation of the investigation into the atrocities at Chusan Camp, Hanaoka, Akita-Ken.