That SN would indicate shipment in the late 1941-early 1942 period (probably the latter), and it would be lend-lease if it has "United States Property" stamped on the top strap. The Lend-Lease Act of 1941 was in effect at that time, and most US military materiel shipped to the allies under lend-lease was marked as being U. S. property (which it legally was). The WB and Ordnance Bomb stamping on the butt is the acceptance mark of Waldemar Bromberg. I am not sure whether he was civilian or military, but he was probably in charge of the Army's Springfield Ordnance District at the time. I've never read anything about him, but his initials appear on these revolvers up to SN (approximately) V151350. He probably did not stamp each revolver himself.
You do have a pre-Victory .38/200 lend-lease service revolver made for the British Commonwealth. 5" was the standard barrel length on these (similar revolvers in .38 Special for US forces use had mainly 4" barrels). Blue would be the correct finish at that time, the hot oxide bluing process used being called "Black Magic." It would probably have received a wire brush surface preparation prior to hot bluing. You will see this finish referred to as a "brush blue." Later, bead or sand blasting was used as a surface prep instead of a wire brush prior to hot bluing, and later still, a phosphate finish (like Parkerizing) replaced hot bluing. That finish started about May 1942. Smooth stocks allegedly started being used very early in 1942. Prior to that they were checkered wood. You are fortunate to have the original matching stocks.
Generally, these revolvers did not have any markings indicating British use. Those that were sold off as surplus after the war received various proof markings. Some commonwealth nations may have applied their own identification stampings at one time or another. Yours, not having the typical post-war proof markings, was likely a duffle-bag bringback by some GI.
You might want to post some pictures. Your pre-Victory is a little out of the ordinary, and worth hanging onto. Many of these were re-bored to accept .38 Special cartridges after the war, but I suspect yours bypassed that fate. And if so, that is very good for value enhancement. You might also check to see that the cylinder and barrel serial numbers match the SN on the butt. They usually will.
