Dear Mr. Kaess,
Thank you for posting your request on History Hub!
We suggest that you submit a Freedom of Information Act (FOIA) request to the US Customs and Immigration Service (USCIS) to obtain a copy of your father’s immigration records. If he did not complete the process, USCIS should be able to provide the certification on non-existence, and although your father won’t have a naturalization record, it is likely that INS did create an A-File that could be used to verify his citizenship status.
We hope this is helpful. Best of luck with your family research!
Below are three pages from an Official Birth Certificate for Gerd Edwin Paul Kaess (Käß), b. Jan 9 1947 in Heutingsheim (Now Freiberg am Neckar), Germany.
Below is a postal envelope addressed to Brian Kaess in Mexico from the Standesamt in Freiberg am Neckar, Germany. It is postmarked 21.05.21 The above three pages of Gerd Kaess' Birth Certificate were mailed inside this envelope.