Dear Mr. Makin,
Thank you for posting your request on History Hub!
The job you describe was typically performed by US Navy personnel assigned as armed guards to Merchant Marine vessels. Also, “Gnr” may be an informal abbreviation for “Gunners Mate” which is a Navy rating for sailors assigned to operate various ship weapons. If he is wearing a uniform in the photo, you may wish to share the photograph to assist us with identifying his branch of service. See How to add a picture to your post or comment for instructions.
We suggest that you request a copy of his Official Military Personnel File (OMPF). OMPFs and medical records of enlisted men of the U.S. Navy who were separated from the service after 1885 and before 1959 are located at NARA's National Personnel Records Center (NPRC), (Military Personnel Records), 1 Archives Drive, St. Louis, MO 63138-1002. To request these records, please mail a completed GSA Standard Form 180 to NPRC. If there is any information requested by the form that you do not know, you may omit it or provide estimates (such as for dates), but the more information you provide, the easier it will be to locate the correct file. For more information, see Official Military Personnel Files (OMPF), Archival Records Requests.
Also, we searched the National Archives Catalog and located the Armed Guard Files, 1934 - 1946 in the Records of the Office of the Chief of Naval Operations (Record Group 38) that may include records of his armed guard detachments. However, these records are arranged by ship name and are not indexed by the names of sailors; therefore, we need to know which ships he served on before we are able to locate relevant records. This information should be listed in his OMPF. For more information about these records, please contact the National Archives at College Park - Textual Reference (RDT2) at Archives2reference@nara.gov.
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. Also, the NPRC is closed except for emergencies. Currently, NPRC will continue servicing requests ONLY associated with medical treatments, burials, and homeless veterans seeking admittance to a homeless shelter. If your request is urgent, please see Emergency Requests and Deadlines. Please refrain from submitting non-emergency requests such as replacement medals, administrative corrections, or records research until NPRC returns to pre-COVID staffing levels. Please check archives.gov/veterans for updates to the NPRC operating hours and status. We apologize for any inconvenience.
We hope this is helpful. Best of luck with your family research!