Russia achieved a creeping advance in Ukraine by forcing ill-trained soldiers into frontal attacks on defended positions.Arkady Budnitsky/Anadolu via Getty ImagesExpendable troops are essential to Russia's costly advance in Ukraine.Criminals allow Russia to expand its army without resorting to a larger mobilization. Convict troops may be more useful in urban warfare than in open terrain or mechanized warfare.To Westerners, the solution was inhuman.