Dear Mr. Pirsch,
Thank you for posting your request on History Hub!
Since “APO” typically stands for “Army Post Office,” it might be helpful to search for the documents using information other than just “APO 696.” According to this article from 2017 that includes images from the report, for example, the cover sheet was signed by U.S. Navy Captain R. F. Hickey on January 24, 1946. The subject of the report is listed as “Investigations, Research, Developments and Practical Use of the German Atomic Bomb,” and the enclosure is labeled “A.P./W.I.U. (9th Air Force) Report No. 96/1945.” We searched the National Archives Catalog and located the series Top Secret Reports of Naval Attaches, 2/1944-8/1947 in the Records of the Office of the Chief of Naval Operations (Record Group 38) that includes the file Document 2644 (Enclosure) - German Atomic Bomb, Commander, U.S. Naval Forces in Europe, London, 24 January 1946. These records have not been digitized. For access to and information about them, please contact the National Archives at College Park - Textual Reference (RDT2) at email@example.com.
Next, we located the series Project Decimal Files, 1941-1945 in the Records of the Army Staff (Record Group 319) that contains a subseries that is arranged numerically by numbered APO (Army Post Office) that includes some intelligence records and reports. These records have not been digitized. Please contact RDT2 for more information about these records.
We also located the series Security Classified Alsos Mission Reports and Correspondence Relating to the Progress of German Scientists in Connection with Nuclear Physics, 1944-1945 in the Records of the War Department General and Special Staffs (Record Group 165) that might contain some relevant information. The series Records Concerning German Nuclear Research, 1946?-1971 in the National Archives Collection of Foreign Records Seized (Record Group 242) also may be of interest to you. These records have not been digitized. Please contact RDT2 with any questions you might have about them.
Plus, we located the series Sources and Methods Files, 1941-2002 in the Records of the Office of Strategic Services (OSS) (Record Group 226) that contains the file Volume 2 - "War Report: Office of Strategic Services: Operations in the Field", which includes discussions of German atomic research and mentions Rugen Island. This file has been digitized and may be viewed online via the Catalog. Please contact RDT2 for additional assistance with these records.
Due to the COVID-19 pandemic and pursuant to guidance received from the Office of Management and Budget (OMB), NARA has adjusted its normal operations to balance the need of completing its mission-critical work while also adhering to the recommended social distancing for the safety of NARA staff. As a result of this re-prioritization of activities, you may experience a delay in receiving an initial acknowledgement as well as a substantive response to your reference request from RDT2. We apologize for this inconvenience and appreciate your understanding and patience.
Finally, the National Declassification Center (NDC) at the National Archives regularly shares NDC Release Lists of records that have been declassified that you may wish to review.
We hope this information is helpful. Best of luck with your research!