On January 30, 1944, United States Armed Forces invaded, but found that Japanese forces had evacuated their fortifications to Kwajalein and Enewetak about a year earlier. A single Japanese warrant officer had been left as a caretaker. With his capture, the islands were secured. This gave the U.S. Navy use of one of the largest anchorages in the Central Pacific. The lagoon became a large forward naval base of operations and was the largest and most active port in the world until the war moved westward when it was supplanted by Ulithi (Yap, Federated States of Micronesia).