The Clone Heavy Trooper (ARC Trooper in Battlefront I) is the Galactic Republic unit built for causing heavy damage to tanks, turrets, and other objects with large amounts of Health. They don't require a very good aim, which is good, considering the shots they have aren't very precise and your target is almost always moving. They can also be used for the disposing of nearby units in one shot (or a few, if they are Heroes), but be careful- these guys do not carry that much ammunition. Due to the weight of the rocket launcher of the Heavy trooper runs much slower then the other classes. (Equivalent to- Assault Droid, Rebel Vanguard, Shock Trooper)
According to The Clone Wars cartoon, the Phase 1 Heavy Trooper should use the RPS-6 Rocket Launcher as the PLX-1 wasn't invented until later in the war, while the original Star Wars: Clone Wars cartoon show units using only the Plex from the beginning to the end of the war.