This Helios brand chronograph has a three pusher Landeron Cal. 47 movement. This caliber was made in the late 1930's. It has an inventory number applied to the stainless snap back. The number appears to have been applied using a rotary tool in a pentagraph, which was a type of tool used by the British back then. While it appears to be a military inventory number, who's military it was and what branch of the military is something of a mystery.

the back

The movement