A surplus mil firearm incl handgun can be imported.
The importation must be done by an 08 or 11 FFL with all the necessary ATf paperwork.
Rifles and Shotguns of Military surplus must be C&R status.
Handguns must be C&R status AND be classed as 'Sporting Firearms'. This latter classification means they must make the ATF Handgun Import Point System for importation.
https://www.atf.gov/firearms/docs/form/factoring-criteria-weapons-atf-form-4590/download
Maybe that's where the old gal fails, In the Point System is the dreaded 'Drop Test'.
It must pass that Drop Test and with the old style hammer block.
I don't know where that stands in the ATF's eyes of concern.
Just remembering the load of Webley MkIV 38's that they allowed in (1990's) but not before a separate crude retro fitted hammer block was installed by the importer.
The letter that the OP received..
"...ATF says: We have come to the determination that the Smith & Wesson model Hand Ejector in .455 Webley is a Surplus Military firearm that is Curio or Relic status of US Origin..."
That is all the letter is saying. A simple statement of what the revolver is.
It's not a Modern Status (post C&R).
But they have come to the conclusion that it is a Military Surplused firearm.
Many I feel would beg to differ. Knowing the history of mfg, with looking at the commercial proofs and lack there of of any Military proof or acceptance markings.
Here's the swipe from the ATF import regs. (kwill1911's document post)
In there it plainly states that Military Surplus handguns are importable IF they meet the C&R status AND the ATF Handgun Import Criteria point system.
".....A surplus military firearm is any firearm which has ever been possessed by a regular or
irregular military force. Surplus military firearms are prohibited from importation under 18
U.S.C. § 925(d)(3); however, § 925(e) authorizes licensed importers (FFL type 08 or 11)
to import surplus military rifles and shotguns classified as curios or relics; and handguns
classified as curios or relics which meet the sporting criteria. In order to qualify for
importation the firearms must be in their original military configuration and cannot have
been sporterized. Further, under the AECA, the importation of U.S.-origin surplus military
firearms is generally prohibited without retransfer authorization from the Department of
State. 27 CFR § 447.57. ....."
Not quick & easy to do, but doable.
There are FFL's that handle this stuff as a specialty. It's expensive and takes time. You must use one of the FFL's to do the importation. Once the gun is here, then they do the OTC transfer to you.
'Sporting Firearms' are handled a bit differently and are somewhat easier to import.