Manni, Saunder's naturalization application was found on ancestry.com searching for Jacob Szuchman, born 1920. The papers were filed in Tennessee 2 Nov 1942. He gives his enlisted serial number as 32164207. He was then in the Army Signal Corps. He lists his name as Jacob Szuchman and is also changing it to Jacques James Saunder. He emigrated to the US on 4 November 1938, arriving on the ship Nieuw Amsterdam, sailing from Antwerp.
https://www.ancestry.com/interactive...258.1525548626
Information on him being in Berlin post war is from some OSS/CIA files. (OSS officers were not impressed with his work in Berlin, and managed to have him removed.) References to Jacques Saunder start on the bottom pdf page 53 and following.
https://ia800303.us.archive.org/10/i...es/Berlin1.pdf
(For those with an interest, there are 6 Berlin files (Berlin1.pdf to Berlin6.pdf) that can be viewed/downloaded, although the 5th file is called BERLIN5.PDF.)
UPDATE: Saunder's officer serial number: O-1997942 found on a roster list here:
http://www.usairborne.be/Roster/ROSTER-505PIR.pdf