A Penal Legion, one of the Legions Penetante, as they are known in Imperial High Gothic, are drawn from Astra Militarum and Planetary Defence Force troops who have committed capital crimes, and had their sentences commuted to life service.
In a desperate universe justice is often harsh and instant, with little consideration given to miscreants and misfits. In the struggle for survival there is no room for individuals who transgress the rigid structures of Imperial society. Such people face servitude for life in the Penal Legions.
There are a great many capital crimes in Imperial Law, so the supply of potential troops for the Penal Legions is never-ending. The Legions are home to killers and psychopaths, to fraudsters and cheats, and to the insane and the fanatic. Pick-pockets and petty thieves rub shoulders with brutal murderers, cackling madmen, and religious zealots.