I'd think it is a civilian M&P if it's chambered in .38 Special. A few were made in .38 Special starting at about that time, as the U. S. wasn't yet a combatant, at least actively. As the vast majority of revolvers coming off the production line then would have been intended for the British contract, I would imagine that virtually all frames at that time had lanyard swivel holes, and they just pulled out and used the same frames for what little civilian production was being performed, the only assembly change being the use of a .38 Special cylinder and stamping a different caliber on the barrel. But I have no way of knowing that.
4 or 5 months ago, I ran across a similar .38 Special revolver with a little higher SN, and it did not have a swivel or hole in the butt. I don't remember the SN, but I believe it was in the low 800000 area.