Along with the rest of the Marshalls, Enewetak was captured by the Imperial Japanese Navy in 1914 during World War I and mandated to the Empire of Japan by the League of Nations in 1920. The Japanese administered the island under the South Pacific Mandate, but mostly left local affairs in hands of traditional local leaders until the start of World War II.

During the Battle of Eniwetok in February 1944, the United States captured Enewetak in a five-day amphibious operation, with major combat on Engebi Islet, the most important Japanese installation on the atoll. Combat also occurred on the main islet of Enewetak itself and on Parry Island, site of a Japanese seaplane base.