Model 3139 Date Confusion

[Gecko10]

I recently acquired a 3139. It has a beautiful patina salmon dial, Mercedes hands, matching the dial patina, "Army" lettered underneath the "Rolex" name, below the 12 'position and a small circular secondhand placed at the bottom of the dial. There are no markings on the outside of the case other than the serial # 231xxx and " Stainless Steel R.M.C and nothing between the lugs.

A serial# lookup says it could be circa 1942 or 1956, after the numbering started all over again.

Any way to tell for sure what year it is without cracking the case?

Thanks