[mrerick]

The P.38 was in use long after they stopped unit marking firearms.

I imagine that they stopped the practice because it shared intelligence with the enemy whenever a firearm or a soldier with a firearm was captured. You knew what unit was or had been in what location!

There was a hierarchy of armorers deployed by military units. Everything from the armorer that traveled with the troops to unit and higher level repair centers. The higher level units had more specialized tools and capabilities, and thus could accomplish more complex repairs. At the lowest level, they could do the more common and basic repairs.