Aggressor

The horrifying bastard lovechild between a Centurion and a Terminator.

"Clad in heavy Gravis armour, Aggressor Squads advance on the foe as walking fortresses of ceramite. More mobile than some other Space Marines, they’re better able to negotiate rough ground, making them versatile troops; while they are often employed in specific circumstances or on certain terrain, Aggressor Squads are used as reserves to plug breaches in gun lines or to spearhead an advance. The range of their weaponry is not too long, but when they get close enough to open fire, the result is a sweeping fusillade of large-calibre bolter shells that can shatter enemy charges."

– Games Workshop

An Aggressor, who is usually a member of an Aggressor Squad, is a new type of Astartes heavy combat support specialist unique to formations of Primaris Space Marines. Aggressors are tasked with heavy short to mid-range fire support and have been outfitted with modified suits of Mark X Gravis Pattern Power Armour refitted to carry shoulder-mounted missile fragstorm grenade launchers that can be automatically reloaded from internal stores within their battle-plate, and fully automatic versions of Guilliman’s bolter/power fist combo. They can also wield Flame Gauntlets (sans grenade launchers) that unleash blazing streams of Promethium upon any foes that get in close; the Salamanders in particular are fond of this setup, and have put it to good use on many occasions. The Iron Hands and Black Templars are also known to employ Aggressors frequently.

Aggressors are basically the Primaris equivalent to the normal Space Marine Terminator Squad or Centurions. However, when it comes to their armaments and defenses, some have basically placed them in-between that of a Terminator and Centurion. Aggressors are noted for their extremely awkward armor even for the standards of Primaris Marines. Whilst it may not be as comically bad as the Dreadknight, it does gain a bitching or two from certain disgruntled elegan/tg/entlemen. This could be due to their bizarrely oversized powerfists that is considered as too cartoony and ridiculous even by the standards of WH40K. Combined the giant fists with the comically skinny legs and the skull covered "rod" hanging between them and you get a unit that will spawn a dozen 'interesting' discussions.

The Aggressor's terminator-esque armor and back-mounted missile launchers are extremely similar to the Cyclone Missile Launcher armed Fulmentarus Terminators of the 30k Ultramarines, meaning that it is likely that Guilliman is re-using his old ideas.

Equipment

Aggressors are armed and armored with the most advance and effective wargear churned out by Papa Cawl and Grandpa Smurf.

Aggressors wear the modified Mark X Gravis Pattern Power Armour which includes an automated loading system for a built-in grenade launcher. Two Boltstorm Gauntllets which is basically a Power Fist that incorporates a Bolter and is used by the Primaris Space Marines, combining a potent melee weapon with the capacity for excellent ranged damage.

For better CQC assaults, they can swap the Boltstorm Gauntlets (and grenade launchers) for the signature Flame Gauntlets which are a new type of Flamer Weapon that practically follow the same design of the Boltstorm Gauntlet. Flame Gauntlets are designed to unleash blazing streams of Promethium upon any foes that get in close. Though their units are intended to provide heavy, long-range fire support, Aggressors use Flame Gauntlets to slay any foes who move into close combat range. Oh yeah, they also carry a Fragstorm Grenade Launcher. Aggressors are a close-range support unit, not a mini Centurion Devastator; they either have the boltstorm gauntlets paired with a fragstorm grenade launcher for 18" dakka, or flamestorm gauntlets for a pair of flamers each as the ranged option.

While fairly close-ranged weapons may seem a bit rubbish, they are all Assault weapons and Aggressors have the Relentless Advance special rule, eliminating the penalty for advancing and firing assault weapons, thus allowing them to move 5+D6" every turn and the only thing they can't do is charge when doing so. Not charging is a valid tactic thanks to the Aggressors' other special rule, Fire Storm, allowing them to fire twice if they don't move that turn. Fancy charging your blob into 3 Aggressors and facing 12D6 flamer hits (or 36+6D6 bolter shots)? Yeah, my gaunts weren't OK with that either. Topping it off their Gravis armour makes these chaps T5 with 3W and a Sv3+, so most small arms fire needs 5s to wound them and you're unlikely to lose one to a lucky shot. Usually.