They were sent to secure military stores provided to an ally, Russia, from potentially being used by Germany against the US and other allies. Their commander was not given clear instructions, and the British Ambassador sent them south, where they fought against the Bolshies.
The infantry units were equiped with Mosin-Nagant rifles manufactured by Remington, rather than with Springfields or Enfields used by most of the rest of the Army. That way they could use the ammunition and spares which they were guarding. The Mosin-Nagant can be in the right hands, a very accurate rifle, but has a slower rate of fire than Mauser, Springfield, Enfield or Lee-Enfield. Better than the Lebel though.
That's just too cool. I own a few 91-30s but never knew there was a Remington version let alone what a Remington version was used for. Thanks for the info!