Update
I received the letter on a Victory which I had posted here before, when I acquired it. V 121 432, unmarked top strap. See pictures below.
A few observations:
The gun shipped some months later than was to be expected based on the serial number. There is another gun, V 157 933, posted earlier in this thread, which shipped to the Maritime Commission at the same location on the same date; S&W apparently collected a batch to ship. As the snip from the U.S.M.C. Annual Report shows, Reading was a receiving warehouse for shipbuilding-related supplies.
The interesting (although unanswerable) question is where this gun actually ended up. It appears unissued. It is not unfired; it has a turn line, and the post-purchase cleaning produced black, but that's likely just from a post-war owner putting some rounds through it. It has no holster wear or scratches, the lanyard swivel is stiff and certainly never swiveled, and there is only one indentation in a grip panel, likely a storage or transport ding.
In April 1943, the Emergency Shipbuilding Program was getting into full swing; it's not like the gun arrived too late to be used. Maybe some manager appropriated it, and it spent the war guarding a desk drawer.