Assault Soldiers are heavily armored members of the Helghast Third Army taking part in the invasion of Vekta during the Killzone campaign. They are slower but stronger than regular Helghast troopers, and are reserved for major attack operations. They're trained in a wide range of Helghast small arms and explosive weapons, and know how to take advantage of emplaced guns. They can use a wide array of weapons on the battlefield.
They are not to be confused with Assault Infantry, who are basic Helghast Troopers reclassified into a new category during the Invasion of Helghan in Killzone 2 & Killzone 3 (as well as Killzone: Mercenary).
Assault Soldiers are even tougher than Elite Soldiers, wearing heavy black/dark-grey armor along with a smooth helmet with an opaque visor. They can withstand roughly 15-20 rounds from the M82 Assault Rifle, and can even survive a direct hit from the BP-02 Pup Grenade Launcher, M327 Grenade Launcher, or Pnv-3 Siska Squad Cannon.
Assault Soldiers wear heavy helmets that allow them to resist headshots; it takes about 4 headshots from the secondary fire of the M66-SD Submachine Gun to kill one, while other enemies with comparative health (namely General Lente's Helghast Bodyguards) die after only 2 headshots from that weapon.
They are typically equipped with heavy weapons, often carrying StA-3 Light Machine Guns, Pnv-3 Siska Squad Cannons, M327 Grenade Launchers, or BLR-06 Hadra MRLs. They are also occasionally equipped with the StA-52 Assault Rifle instead, usually in close quarters such as aboard the orbital SD platform. Their tendency to wield heavy explosive weaponry, combined with their heavy armor, can make them a significant threat.
Assault Soldiers first begin to appear in Mission 6: Misty Waters. Usually, a single Assault Soldier will be supporting a squad of Helghast Troopers or Elite Soldiers with heavy weapons fire. They are quite rare for most of the campaign, with only a handful appearing throughout Mission 6 to Mission 9. They become more common in the game's last two missions, where the majority of them are encountered. Overall, a total of roughly 35 Assault Soldiers appear throughout the entire campaign, although this varies slightly depending on which character you play as.
In the campaign of Killzone 2 and Killzone 3, the role previously filled by Assault Soldiers have been divided among a number of new Helghast unit types, namely the Support Troopers, Grenadiers, and Commandos.