This 'winter' soldier is standing at-ease with his M1918 Browning Automatic Rifle by his side.
The B.A.R. was one of a family of American automatic rifles that entered service late in 1918 and continued throughout WW2, the Korean conflict and even as late as the Vietnam War!
Utilizing a 20-round box magazine the B.A.R. fired the standard 30-06 round (the same as the WW1 '03 Springfield Rifle'). Eventually in 1957 it began to be replaced by the machine gun as the standard S.A.W. Squad Automatic Weapon.