Final answer:
The SS Special Action Squads targeted Jews and other groups viewed as undesirable, killing them primarily through mass shootings and later with gas vans and gas chambers.
Step-by-step explanation:
The victims of the SS Special Action Squads, also known as the Einsatzgruppen, were primarily Jews, but they also targeted political dissidents, Roma (gypsies), the mentally and physically disabled, and others deemed undesirable by the Nazi regime. These mobile killing units executed their victims mainly through mass shootings, forcing them to dig their own graves before being shot at the edges of ravines or mass graves. To further optimize the mass murder process and reduce the psychological impact on the shooters, the Nazis later developed gas vans that killed through carbon monoxide poisoning, and eventually established extermination camps with gas chambers using Zyklon B and other methods of asphyxiation.