"Shock troop" is a calque, a loose translation of the German word Stoßtrupp. Military units that contain assault troops are typically organized for mobility with the intention that they will penetrate enemy defences and attack into the enemy's vulnerable rear areas. Any specialized, elite unit formed to fight an engagement via overwhelming assault (usually) would be considered shock troops, as opposed to "special forces" or commando-style units (intended mostly for covert operations). Both types of units could fight behind enemy lines, by surprise if required, however.