canadian provost 

18th Armoured Car Regiment, 12th Manitoba Dragoons
http://douglasfisher.ca/bio/soldier/
Interesting read of a soldier's life.

18th Armoured Car Regiment, 12th Manitoba Dragoons

Two Princess Patricia’s Canadian Light Infantrymen, 1CID in a slit trench at Spinete, Italy, 22Oct43. An M-1 TSMG can be seen with the butt unscrewed. This was commonly done to reduce length and weight during night patrols, as most shooting was at extreme close range and the fire-arm acted as a fully-automatic pistol with a large capacity magazine.
Butts of the M-1928 versions were readily detached and re-attached using an integral push button; however, M-1 butts had to be unscrewed to remove. 
(LAC, PA16374)