The Imperial Shock Trooper is an infantry unit available to all Imperial factions, specializing in anti-armor. Each squad is made up of 3 troopers, and each trooper is armed with a PLEX Missile Launcher.
The Imperial Shock Trooper descended from the earlier Clone Shock Troopers of the Galactic Republic. Upon the reformation of the Republic into he Empire, the Shock Troopers retained most of their previous duties: to guard the capital and to be deployed on special, often hazardous, assignments. To accommodate these special assignments, Shock Troopers were often given specialized weaponry not often assigned to normal Stormtroopers. They would see action in a variety of battlefields. Some were even members of the 501st Legion.
Although nearly all the Shock Troopers were killed during the Galactic Civil War, the Empire managed to survive (as the Imperial Remnant). Over time, they would rebuild their military strength and skill. By 40 ABY, the Shock Troopers' efficiency had risen to the level of the Empire's 501st.
The Shock Trooper is the anti-armor infantry of the Imperial factions. Think of them as an Imperial counterpart to the PLEX Trooper of the New Republic and use them, basically, the same way. However, they only come in two squads of six, so they should always have Stormtrooper support (as kind of a meat shield).
They are very effective against anti-vehicle units but don't do alot of damage to infantry. They will get massacred by anti-infantry vehicles without support. In short, the Shock Trooper is an anti-armor support infantry that is best used behind Stormtrooper ranks.