A BRIEF POSTAL HISTORY OF THE U.S. TRUST TERRITORY OF THE PACIFIC - WW 2 TO 1951
Prior to World War II the Caroline and Marshall Islands and the Northern Mariana Islands were administered by Japan under mandate from the League of Nations. The Southern Mariana island of Guam was however administered by the U.S.
Guam was captured by the Japanese on December 10, 1941.
During 1944 as U.S. forces rolled across the Pacific the whole of the Caroline, Mariana & Marshall Islands came under U.S. military control. The postal services on Guam were returned to civilian control by December 1944 but in the rest of the area postal services were provided by the U.S. military.
On July 19 1947 the former Japanese administered islands were transferred in trust by the United Nations to the jurisdiction of the United States. They were known as the U.S. Trust Territory of the Pacific.
Initially the civil administration was under the U.S. Department of the Navy and postal facilities were operated by military personnel using standard military APO/Navy Branch P.O. type cancellations. The exception was Koror in the western Caroline islands which for a short time during 1947 used cancellations reading "U.S. MILITARY GOVT. UNIT/PALAU ISLANDS"
U.S. Navy at Majuro::::::::::::::::::::::::U.S. Military Government Unit at Palau
On July 1 1951 responsibility for the civil administration of the islands was transferred from the U.S. Department of the Navy to the U.S. Department of the Interior - the islands were now under civilian administration and the U.S. Post Office was ready to open Post Offices.