The 48th CA was in western pacific, and was inactivated in Hawaii in 1945 looks like the consolidated. 48th Field Artillery of the 7th Infantry Division.
Dear Mr. Johnson,
Thank you for posting your request on History Hub!
The Participation in the Western Carolines and Central Philippines operations document that we linked in our previous reply is word searchable and contains two references to APO 264, the second referring to “AGF, APO 264 (Angaur)” indicating that this was the Army Garrison Force for the island of Angaur, also known as Ngeaur Island.
Additionally, we located the Order of Battle of the United States Army Ground Forces in World War II Pacific Theater of Operations that includes several references to the organization which also indicate it was the garrison force for Angaur, with a portion of page 155 dealing specifically with the unit. This document also provides additional information about the capture of the island. An initial search of the document does not reveal information about the specific coast artillery and field artillery units you are researching, however there may be something we missed when we reviewed it.
The World War II Operations Reports, 1940 - 1948 referenced in our previous may provide additional insights. In addition, we searched the National Archives Catalog and located General Correspondence Files, ca. 1942 - ca. 1954 in Records of U.S. Army Operational, Tactical, and Support Organizations (World War II and Thereafter) (Record Group 338) that includes the file 322: Orders and Plans, 81st Infantry Division, Angaur Island, 5 August 1944; Unit Histories, 1943 - 1967 in Record Group 338 that include the files Headquarters, Army Garrison Force, Army Post Office 264: Memorandums and Headquarters, Army Garrison Force, Army Post Office 264: General Orders; and Background Files to the Study "The Palau Campaign", 1944 - 1947, Background Files to the Study "History of the Palau Islands", 1946 - 1948, and Background Files to the Study "The Approach to the Philippines", 1945 - 1958 in the Records of the Army Staff (Record Group 319). For more information about these records, please contact National Archives at College Park - Textual Reference (RDT2) via email at Archives2reference@nara.gov.
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We hope this is helpful. Best of luck with your family research!