I think the barrel is a 5-incher, which suggests that the gun
may be an .38/200 British Service Revolver aka "British Victory" produced for the British military early in WWII when S&W was still finishing these guns in a glossy rust blue rather than grey-black matte phosphate. The lanyard loop usually indicates a military gun.
Other hallmarks of such a gun will be a *.38 S&W CTG.* (rather than *.38 S&W SPECIAL CTG.*) barrel rollmark, numerous small crown-over-BNP proof marks, and a serial number in the high six-digit range with no alphabetical prefix. S&W added a "V" prefix when production numbers surpassed 1 million, but most of these guns have the aforementioned matte phosphate finish.
It appears, however, that the cylinder is a replacement.
Agreed, perhaps to allow .38 Special ammo to be fired. The British guns were almost all chambered in .38 S&W, a shorter, slightly larger-caliber, and less powerful cartridge that fell out of favor in the postwar era.
On a S&W of this vintage, the serial number*- or at least the last several digits- should be repeated on the cylinder face and on the barrel flat over the ejector rod. Differing numbers in these places indicate replacement parts.
In addition to the cylinder, I think the stocks (grips) may be replacements from a different gun, because they don't appear to have a factory-perfect fit at the top of each panel around the medallions. Until the 1970s, S&W stocks were shaped to fit individual guns, and the fit was usually almost seamless.
[*Edit to add footnote: The serial number on a medium-frame S&W swing-out cylinder revolver is found on the butt. The number inside the yoke cut in the frame is normally a meaningless assembly number.]