The first of three expansion packs to Warhammer 40,000: Dawn of War, Dawn of War: Winter Assault continues to bring Games' Workshop tabletop of the same name to life, this time giving players control over the Imperial Guard. While they were seen and occasionally playable during the first title, this expansion makes them their own playable race, separate from their Imperial brothers, the Space Marines. The mission-based campaign system returns in Winter Assault as well, with two different stories. Players can influence the story by making choices as how to progress through the story, ultimately affecting how the story ends. Many changes have been made to the returning races, mainly to balance out each faction. The most obvious change is that some units are now capped, preventing players from making excessive amounts of units. In other cases, the types of wargear that a squad can be equipped with have been changed or removed and some unit abilities and upgrades have been wiped from some races entirely.
Winter Assault was followed up by Warhammer 40,000: Dawn of War - Dark Crusade, which established which endings were accepted as canon at the conclusion of Winter Assault.
The Imperial Guard act as the main army of the Imperium, with billions enlisted. The Guard isn't an entirely uniform organization. While there is central leadership, forces that make up a guardsmen detatchment in a region depend mainly on the people inhabiting the planets on that system. The Imperial Guard as seen in the 41st Millennium was created along with the Space Marine Chapters in the wake of the Horus Heresy. In an attempt to break up the Imperial Army, the Guardsmen and the Imperial Navy were separated into two different forces of the Imperium. The Guard is not comprised of superhuman soldiers, instead these are the normal citizens of the Imperium that have taken up arms in order to defend the Imperium from the many forces that threaten it.
In Winter Assault, Imperial Guard act as a defensive "turtling" race that build up huge defenses and create defensive lines that allowed them to "tech up". What the guardsmen lack in strength and modifications that the Space Marines have, they make up for in numbers.
Winter Assault has two campaigns, each with their own storyline, but the overall objective is similar between the two campaigns. In both campaigns, players take control of one of four races and fight to take control of an Imperator-class Imperial Titan. In the first campaign, titled "Forces of Order," the 412th Cadian Guardsmen regiment lands on Lorn V to assist Ultramarines already engaging foes on the surface. The Guardsmen, with some help from the Eldar eventually make it to the Space Marines and meet up with the Titan crew sent to pilot a crashed Titan discovered on the planet. Because of a local group of Orks, the Eldar are discovered by the Imperial Forces, but Farseer Taldeer tells General Sturnn that the Eldar do not seek the Titan, but rather something that lies beneath the surface of Lorn V: the Necron, an ancient race of immortal, robotic servants of the C'tan. At this crossroad in objectives, players are given the choice of taking control of either the Eldar or the Guardsmen and see their personal objectives completed. In the campaign of Disorder, players play primarily as Warlord Gorgutz of the Orks as he attempts to unite the Orks and begin a "Waagh!" across the planet. But before he can start his Waagh! in its entirety, he encounters Chaos forces and must fight them in order to continue his plans.
In an attempt to balance and refine the Dawn of War gameplay, a number of tweaks have been made to the existing races:
- Universal weakening of Tier 1 units as well as speedier researches for the tech tree encouraged games to last for much longer than in the previous incarnation of the series
- Later Tier units effectively replaced lower tier units, making them redundant resulting in even more emphasis placed on a player's ability to research their HQ and prevent the opposition from doing likewise
- Relic Units (The Bloodthirster, Squiggoth, etc.) were beefed up and their costs were reduced to make their importance and therefore appearances more common in Multiplayer
- Reorganization of the unit tech tree, such as moving the Chaos "Possessed Chaos Marine Squad" to Tier 3 when they had previously been Tier 2.
- Space Marines: Chaplain (Commander unit specializing in close combat, passive abilities, and breaking enemy morale
- Eldar: Fire Dragons (Fast-moving, short-ranged, anti-armor unit)
- Chaos: Khorne Berserkes (Chain-axe wielding, close combat specialists)
- Orks: Mega Armoured Nobz (Secondary commander squad)