A recent documentary on History channel on the battle of Stalingrad described the penal units.
They were formed from prisoners, in the case of the guy interviewed, he was in jail for protesting the removal of a teacher who criticized stalin. sent to the gulag. then to a 'penal unit'. The Russians used the units a "reconnaissance by attack" - they'd send the unit in, and depending on how and where the unit got shot at, the Russian general knew what they were facing. Literal cannon fodder.
The penal unit 'soldier' interviewed said you were just numb to your destiny, death was inveitable. The death rates were over 90%, this particular man somehow was a survivor.
It is stuff like this that explains how Stalin managed to lose 20 million men fighting a German army a fraction of that size. One can say the deaths are due to Hitler because Hitler attacked Russia, but in reality it was due to Stalin - rather than kill folks in the gulag, he let the German bullets do the dirty work for him.
Just another reason Stalin edges out Hitler as the world's worst Murderous-Evil-Dictator.