Tony,
Your gun certainly falls within a SN range of lettered Navy guns. Shipping date is estimated as July/August, 1942.
I presume it's a typical 4" with parkerized finish & smooth stocks; I also gather it has "U.S. NAVY" on the left top strap, but how about any other markings? Navy guns of this period don't typically have additional markings, such as the "P" proof or "W.B." initials on the butt, but I always ask.
Please let us know when you get Roy's letter so that we might enter his info into the database. TIA!
Steve