A group of Marines having a smoke while checking out what looks to be a shell and fuse for either an 81mm mortar or 75mm howitzer.
Dig the M1917A1 Brodie helmets with EGAs, sewn-on stripes on light khaki uniforms, and the top-charging M1928A1 Thompson submachine gun. The Tommy gunner also has pretty bad trigger D and what looks to be a set of wire cutters in his five-cell stick mag pouch. At least there isn’t a mag in the Chicago typewriter.
I can’t find a full-fledged source for the image, but reverse sources are all Chinese-language pages for 1938 Shanghai, a tense place and period in history as the country was torn between the Reds and KMT while under aggressive attack by the Empire of Japan as the rest of the world stood by to wish the Chinese the best of luck.
These men are likely of the 4th Marine Regiment, the famed “China Marines” stationed in Peiping, Tientsin, and Shanghai from 1927 to 1941. Pulled out of the continent only weeks before Pearl Harbor, they were withdrawn to the Philipines just in time to defend Bataan.
There is this great follow-up picture of these Devils.