pre war Camp Perry accessory

[FlightRN]

Good Day All,
My Grand-Uncle (Maj. Rex Z. Michael) served in WW2, Korea (Chosin) and was on the USMC shooting team where he served as 1956 3rdMarDiv. Team Captain. Years ago,before he passed, we spoke about his time on the team and he gave me this P.J. O'Hare micrometer and stated it belonged to a shooting friend who was part of the Marine contingent aboard the U.S.S. SARATOGA (CV-3) during WW2. Given my Grand Uncle's history and other interesting bits in his shooters boxes, I tend to believe the story.
Its conjecture but I posit the electro pencil engraving was applied when the ship was decommissioned as a reminder of the original owners time on the ship. In July 1946, the ship was a target for nuclear weapon tests during Operation Crossroads and sunk.
I am curious about the "U.S. 812". I recall seeing another micrometer with similar stamped numbers and only surmise it was a way of accounting for the item. Does anyone know another reason for this marking?
Regards,
Michael