Abstract Lack of terrain data contributed significantly to the high costs of lives and operations during the Pacific campaign of World War II. After the war the U.S. Army Corps of Engineers contracted with the Military Geology Branch of the U.S. Geological Survey to gather detailed terrain information about the occupied islands under direct U.S. jurisdiction in the event they or comparable oceanic islands became sites of future military operations. The U.S. Geological Survey established a headquarters in Tokyo and initiated field studies of Okinawa during 1946. Subsequent detailed studies were launched at the Palau Islands (1947), Yap Islands (1947), Saipan (1948), Tinian (1949), Guam (1951), Pagan, Marianas Islands (1954), Truk (1954), Ishigaki and Miyako (1955), and the Marshall Islands (reconnaissance, 1951). Initial plans for detailed studies of all mandated islands were abandoned for lack of time, but members of the field parties briefly visited nearly all. Field teams included geologists, hydrologists, soils scientists, a plant ecologist, and a climatologist. The Tokyo office gathered and translated existing Japanese literature about the islands; more than 600 articles were translated. A by-product was the establishment of a joint U.S.-Japanese project to compile and publish a series of 1:250,000 geologic maps of formerly held Japanese territories, including Korea, Manchuria, northeast China, southern Sakhalin Island, and the Kuriles. Results of the field studies were published in a series of military geology folios composed of both basic and interpretive chapters. U.S. Geological Survey professional papers presented many of the scientific results.