Soldiers, criminals and civilians sentenced to those units were generally poorly armed and required to undertake dangerous high-casualty missions.

The Strafbataillon, which were under the control of the Feldgendarmerie, were then used to conduct dangerous operations (sometimes akin to suicide missions) for the Heer, such as clearing minefields, assaulting difficult objectives and defending positions against overwhelming attacking forces.

Initially, Nazi policy was to rebuild the armed forces by keeping "potential troublemakers" away from the troops and removing any "destructive elements" from military service.

But on 21 May 1935, Adolf Hitler decreed that under the new Nazi Defence Act, any conscript who was deemed "unfit for military service because of subversive activity" would be arrested.

Military tribunals were directed by the OKW to send incarcerated members of the Wehrmacht, as well as "subversives", to Bewährungsbataillone (English: probation battalions) at the front.

The order stated that any first-time convicted soldier could return to his unit after he had served a portion of his sentence in "a special probation corps before the enemy".

Beginning in April 1941, convicted soldiers – even those sentenced to death – who had shown exceptional bravery or meritorious service, were allowed to rejoin their original units.

In October 1942, the 999th Light Afrika Division was formed from civilian criminals and prison inmates who had been deemed "unfit for military service".

In September 1944, some troops from the 999th, including Falk Harnack and Gerhard Reinhardt, took active part in armed resistance with the Greek Liberation Army (ELAS).

Possessing the direct authority from the OKW, they had the power to maintain control and discipline throughout all the German armed forces including the SS.

The critically acclaimed Soviet war drama film Come and See has parts which depict Holocaust warcrimes by Nazi troops, including penal units.