I'm guessing these guys were popular in those long, cold nights.
From the article:
The ROKS-2 was a man-packed flame-thrower used by the Red Army throughout the duration of the Second World War. It had a unique design feature in the fact that the man carry it was meant to resemble the rest of his comrades in arms.
The fuel tank was designed to resemble a regular rucksack and the flame projector itself the standard military rifle of the Red Army, the Mosin–Nagant 91/30. It was theorised that in the heat of battle the enemy would not be drawn to it until it could be brought to bear.