Rick Priestley explained that this was to illustrate the Imperium's practice of erasing embarrassing or incriminating events and figures from Imperial records (damnatio memoriae).

In terms of playing style, a Space Marine army neither excels nor fails at any particular tactic, though certain Chapters do have variant rules (e.g. the Salamanders specialise in flamethrowers).

Individual units are typically not strongly specialised and can roughly substitute in other roles, meaning most mistakes and setbacks are easy to compensate for.

Their tough armour and generally unspecialised weaponry means that they do not have to be maneuvered as carefully as units of other armies (such as the powerful but frail Aeldari).

Players are also required to declare their allegiance, whether they are loyal to the Emperor of Mankind (Loyalist), to the Warmaster Horus (Traitor), or occasionally, something else (Blackshields + Shattered Legions).

The archetypal Space Marines in game lore and miniature variety don protective exosuits known as Power Armour.

Bob Naismith created the initial design of these Space Marines for the first edition, with the helmet having a gas mask with an airtube connected to the snout, and this was used for a 1991 limited release model.

However designers at Games Workshop felt that this concept was too banal and derivative, and they made a conscious decision to give the Space Marine, and Warhammer 40,000 in general, a "medieval-in-space" aesthetic, so the exosuit was redesigned to resemble medieval plate armour.

The 3rd edition featured unique plastic Terminators designed specifically for Space Hulk, instead of being shared with the sets for the tabletop game Warhammer 40,000.

A Space Marine is created by implanting "gene-seed" in a human recruit, which transforms them into superhuman soldiers by severely altering their organism.

Fully developed Space Marines have two functioning hearts, three lungs and an additional kidney in order to sustain their improved metabolism, together with a series of other genetically-engineered organs that serve various purposes.

Space Marines wear suits of mechanised armour, which has a medieval aesthetic where heraldry is often brightly painted and ornately decorated (camouflage, while still useful in warfare of the far future, offers little to no benefit for Astartes who are best used as shock troops and in direct assaults), with several types depending on their rank/experience and combat roles.

Those that successfully pass all tests become full-fledged Marines, earning the right to wear a suit of Power Armour which is environmentally sealed and cybernetically enhanced, and which provides a balance of resistance against most anti-infantry firepower while retaining quick reflexes making them flexible for numerous frontline situations.

However, Terminators are slower and there are limited means to deploy them upon the battlefield (either being transported in the Land Raider main battle tank/infantry fighting vehicle, or being teleported).

The Dreadnought, often confused as an extra-large fighting suit or robot, is actually a powerful cyborg battle walker with a mortally wounded Marine entombed permanently inside the sarcophagus.

[18] Space Marines can live for centuries and thereby develop vast combat experience, with veterans (Terminators and Dreadnoughts) being the most highly-honoured among their peers.

Each Space Marine Chapter is a fully integrated military force, with space-faring vessels emphasizing planetary landing/assault (as opposed to Imperial Navy warships for space combat), while Marine vehicles emphasis rapid mobility for rapid deployment (as opposed to the Imperial Guards' equivalents which are typically designed with heavy firepower and/or thick armour at the cost of speed).

The Space Marines themselves are dedicated shock troops, while ordinary human serfs serve in support roles such as crewing their ships and maintaining their equipment.

The creator of the Codex Astartes, Roboute Guilliman, who was also the Primarch (genetic "father") of the original Ultramarines Legion, had allowed the creation of a new generation of Space Marines after the events of the Horus Heresy.

When Guilliman was resurrected ten thousand years later, Legions of Primaris were introduced into the Imperial forces to augment the existing Chapters and create new ones.

A few centuries into this campaign, fully half of the Space Marine Legions converted to the worship of Chaos and rebelled against the Emperor.

For instance, Chaos Space Marines devoted to Nurgle have grotesque, bloated bodies riddled with disease, yet are paradoxically very resilient in battle; whereas Chaos Space Marines devoted to Slaanesh are obsessed with pleasure and beauty, but are hideously deformed and push physical and mental sensation to limits that a normal human would consider to be sheer torture.

Although Chaos Space Marines are just as likely to fight amongst themselves as they are against loyalist forces, on occasion they will unite and form a “Black Crusade,” with the explicit purpose of defeating the Imperium and slaying the “False Emperor” once and for all.

None of these Black Crusades have yet achieved their main goal, but have managed to cause great damage in Imperial space and allowed Chaos forces to steal valuable technology and information from the Imperium.

Space Marines are featured in numerous Science-fantasy novels, predominantly published by Black Library, a division of Games Workshop.

[20] The row received a lot of publicity during February 2013, with authors such as Cory Doctorow, Charles Stross, and John Scalzi supporting Hogarth.