It is both. The 38/200 was the UK service cartridge in the WW II period. It is virtually the same as the US 38 S&W 200 gr bullet loading sometimes referred to as the Police load.

Although all whether of the Lend/lease or British Contract revolvers destined for England/Commonwealth countries made by S&W were referred to by the Smith factory as the 38/200 British Service Revolver model, they were marked 38 S&W.

Lend/Lease guns were stamped US Government or Property of US Government IIRC and many inspected/stamped by GHD. US service arms were typically stamped with the flaming bomb.

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Jim
S&WCA #819