The .38 S&W is a revolver cartridge developed by Smith & Wesson in 1877. Though similar in name, it is not interchangeable with the later .38 Smith and Wesson Special due to a different case shape and slightly larger bullet diameter.
The British military adopted a loading of this cartridge as the Cartridge, S.A., Revolver Ball, 380 in, MkI .38-200, with the "200" referring to the weight of the bullet in grains. In 1937, this cartridge was replaced in British Service by the Cartridge, S.A., Revolver Ball, 380 in, MkII. The main difference between it and the previous round was that that it had a 178 gn. FMJ bullet.
