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"Such is the woe cast upon the Domains of the God-Emperor of Mankind in these times that in their wisdom and beneficience, the High Lords of Terra have this day issued this decree: Let there be a Founding of the Adeptus Astartes, and let the foes of the Emperor know that this galaxy belongs to Him, now and forever."

— High Lord Tagus, Convenor of the 349th Congress of the Imperium
UM Chapter

The Ultramarines, the archetypal Codex Astartes-compliant Space Marine Chapter, gathered for war.

A Chapter is a completely autonomous military unit made up of one thousand transhuman warriors known as Space Marines and their related vehicles, starships and support personnel. Each Chapter serves collectively with the others of its kind as part of the Imperium of Man's Adeptus Astartes. Every Chapter is entirely autonomous from every other adepta of the Imperium, including the Inquisition, and takes its orders only from the High Lords of Terra themselves.

Most Chapters have feudal title to an entire planet of the Imperium which serves as its Chapter homeworld or to a large fleet of powerful and massive starships that serves as a mobile headquarters if the Chapter is fleet-based.

The majority of Space Marine Chapters follow the dictates of the Codex Astartes, a sacred tome written by the Ultramarines Primarch Roboute Guilliman. The Codex Astartes details the proper organisational structure and mobilisation methods for a Space Marine Chapter. The Codex has been adopted by the vast majority of Space Marine Chapters as their organisational blueprint.

Consequently, most Space Marine Chapters are considered "Codex Chapters" or "Codex-compliant Chapters" due to their adherence to the Codex Astartes. It is believed that there are about 1,000 Chapters of Space Marines operating throughout the galaxy at any one time, though this number can fluctuate greatly as time and circumstances determine.


During the Great Crusade in the late 30th Millennium, the Space Marines were originally organised into 20 Legions each of which was further divided into companies. The XIII Legion, the Ultramarines, led by Roboute Guilliman, became the largest of all the Astartes Legions as a result of Guilliman's tactical mastery and a steady flow of new recruits from the Realm of Ultramar as well as the terrible losses suffered by other Legions such as the Dark Angels during the Rangdan Xenocides.

The Ultramarines became so large, growing to a size that included over 100,000 Astartes, that a new, larger unit of division, the chapter, was created to better organise the XIII Legion's forces. This form of organisation was also adopted by many of the other Legions of comparable size.

These chapters, alternatively designated as great companies, harrows, millennials, etc., depending on each Legion's particular culture, were originally composed of roughly 1,000 line Legionaries, but as the Legions grew, this number began to vary substantially by Legion, and also through the vicissitudes of war and the availability of replacement recruits. At the time of the outbreak of the Horus Heresy in the early 31st Millennium, the Ultramarines Legion was divided into twenty Chapters, each composed of ten companies, with each company composed of roughly one thousand Astartes.

Following the end of the Heresy, Guilliman, as the new lord commander of the Imperium, ordered during the event known as the Second Founding that the remaining Loyalist Space Marine Legions be divided and re-organised into smaller, one-thousand Space Marine Chapters, to ensure that no future rebel such as Horus could gain control of such a large and power military unit as a Space Marine Legion again. Newly-formed Chapters created at this time that were carved out of the remaining 9 Loyalist Legions became known as Successor Chapters.

As a result of this change in organisation, the Space Marines' military purpose changed as well. Where the Space Marine Legions had once served as the Imperium's primary frontline military forces, that role was given over to the newly created Astra Militarum, which had been created from the remains of the Imperial Army in the wake of the Heresy.

The Imperial Army had been used primarily as a reserve force of garrison troops during the Great Crusade, but its successor would now bear the primary burden of the Imperium's defence. In the wake of the Second Founding, the Space Marine Chapters were intended to primarily serve as highly mobile planetary assault and special forces troops, who would be deployed only for the toughest missions confronting the Imperium for which the forces of the Astra Militarum were simply insufficient.

Chapter Founding

New Space Marine Chapters are not created piecemeal as required by the Imperium's strategic needs, but rather in deliberate groupings called "Foundings." The process by which a new Founding's creation is approved by the Imperial government is mysterious and arcane, subject to decades or even centuries of planning before it is announced. It is only by an edict of the High Lords of Terra that such an undertaking as the creation of new Chapters can be instigated, for it requires the cooperation and mobilisation of countless divisions within the Imperium's monolithic and vast governmental organisations. Establishing new Astartes Chapters on an individual basis is nigh impossible--the mobilisation of such vast resources is beyond the ability of any single segment of the Imperium.

The Adeptus Mechanicus plays an essential role in the process of a Founding, for its highest echelons are tasked with creating, testing and developing the gene-seed samples that will provide the genetic foundation of the new Chapters. By ancient custom, the Mechanicus has the right to expect a tithe of 5% of the gene-seed of every Space Marine Chapter to assist it in the creation of new Chapters and to check that the purity of the existing Astartes Chapters' DNA has remained untainted by mutation or exposure to Chaos.

Each Chapter is created from the gene-seed of an existing donor Chapter. The zygote derived from each type of gene-seed is implanted by the Magos Biologis of the Adeptus Mechanicus in a human test-slave who spends his entire life in a static experimental capsule, immobile and serving as nothing but a medium from which two Progenoid Glands will develop. When the Progenoids are fully developed, they are extracted from the original test-slave and then implanted into another two test-slaves, producing four Progenoids, and so on.

It takes 55 Terran years of this type of reproduction to create a healthy set of 1,000 new Astartes organs. These must be tested for purity and genetic consistency before they will be sanctioned officially by the Fabricator-General of the Adeptus Mechanicus and then by the High Lords of Terra, speaking for the Emperor of Mankind, who alone can give permission for the creation of a new Chapter.

Entire Forge Worlds may be turned over to the manufacture of the mighty arsenal of weaponry, ammunition, Power Armour, vehicles and starships that any such force will require. There are a myriad of other concerns as well. A suitable homeworld inhabited by humans must be identified for the new Chapter, which will likely provide not only a secure and defensible base of operations, but also a source of new recruits as well. Such worlds might have been reported by itinerant Rogue Traders and earmarked centuries before by Adeptus Mechanicus Explorators as potential Astartes homeworlds. A degree of environmental terraforming might be required and the natives of the world (if they are to become the source of the new Chapter's Aspirants) must be studied and tested by the Mechanicus' Magi Biologis and Genetors for many generations to ensure they are genetically pure and free of any strain of mutation that might later affect the Chapter itself.

The construction of a Chapter's fortress-monastery may be one of the greatest undertakings of all, drawing on the genius of the Imperium's most accomplished military architects and engineers. If the Chapter is to be fleet-based, then even more work must be put into the construction of a massive Chapter Barque or an unusually large Battle Barge to serve as the Chapter's mobile fortress-monastery and all of the related capital warships and Escorts such a highly-mobile Chapter will require.

The already extant Space Marine Chapters may also have a role in this process, though to what degree can vary greatly from Founding to Founding. Many of the First Founding Chapters maintain close links with Chapters created using their own gene-seed stocks, and the Chapter Masters might have a hand in planning future Foundings using that genetic material. It is said that the Disciples of Caliban, a Dark Angels Successor Chapter, was created following the direct appeal of the Supreme Grand Master of the Dark Angels, an extremely rare request.

In the more than 10,000 Terran years that have passed since the First Founding of the 20 original Space Marine Legions by the Emperor, there have been 26 subsequent Foundings of new Chapters of the Adeptus Astartes; with the most recent, the Ultima Founding of the Primaris Space Marines, occurring in the year 999.M41 at the time of the birth of the Great Rift.

Even before a new Founding is announced, entire generations of Imperial servants may have toiled in preparation. Even once the process has been declared and is underway, it is likely to be at least a standard century before the new Chapters are ready to begin combat operations.

In times of dire need for the Imperium, faster development has been attempted, but this has often resulted in disaster. Gene-seed cultured in haste is likely to degrade or to mutate, and a great many other factors can lead the entire process astray. And there is no foe more dangerous to the Imperium of Man that a Space Marine who has been corrupted by Chaos or gone Renegade for another reason.

Traditional Chapter Organisation

Chapter's Hierarchy

Traditional Space Marine Chapter's Hierarchy

Each Codex-compliant Space Marine Chapter before the era of the Great Rift consisted of 1,000 fighting Space Marines plus support staff which are divided into 10 companies. Each Chapter is led by a Chapter Master. Unlike the Astra Militarum, the Adeptus Astartes has no leadership above the Masters of the individual Chapters. Also unlike many other Imperial military forces, the Astartes has no members to represent the organisation as a High Lord of Terra on the Senatorum Imperialis.

Each of the ten companies of a traditional Chapter is comprised of one hundred Astartes, led by a Captain -- a veteran officer of countless wars. A company is organised into ten squads of ten Space Marines, each led by a Sergeant.

Besides the Space Marine fighting brethren, there are many non-combat personnel, fully part of the Chapter but generally not involved directly in combat. These include the Chapter's hereditary slaves or bonded Chapter Serfs, Astropaths, Navigators, etc.

The following outline defined all Codex-compliant Space Marine Chapters until the Ultima Founding, when the creation of all-Primaris Space Marine Chapters and the heavy reinforcement of existing Space Marine Chapters with Primaris Astartes altered this traditional organisational scheme for the first time in 10,000 Terran years.

Headquarters Staff

Each company of a Codex-compliant Chapter before the Ultima Founding had its own command or headquarters staff, consisting of at least one of the following:

Most companies were usually accompanied by a Command Squad of five Veteran Space Marines that included:

  • Company Captain
  • Company Champion
  • Apothecary - For a Space Marine Chapter to have a future it must carefully protect and preserve the organic implants created from gene-seed that turn an Aspirant into a full-fledged Space Marine. An Apothecary serves as a Chapter medic and biological researcher and the overseer of the Chapter's gene-seed and implantation process for the creation of new Space Marines.
  • Ancient - Ancients or Standard Bearers were Veteran Astartes who carried the company banner that displayed the company's feats and prowess. Captains may also display their personal heraldry in the banner. On rare occasions, the Chapter Banner might be fielded by a particular company's Command Squad.

Company Structure

UM Astartes Ultra

The traditional order of battle of the Ultramarines, the archetypal Codex Astartes-compliant Space Marine Chapter, displaying the full composition of all ten companies before the introduction of the Primaris Space Marines during the Plague Wars.

The 1st Company of any traditional Codex-compliant Space Marine Chapter was an elite force made up entirely of Veteran Marines. These skilled warriors are the only members of the Chapter trained in the use of Terminator Armour.

The 2nd  to 5th Companies of the Chapter are referred to as Battle Companies and serve as the Chapter's frontline combatants. Each Battle Company consists of:

The 6th to 9th Companies of a traditional Space Marine Chapter are its Reserve Companies. These are entirely composed of squads of the same combat specialty designation. For instance, the 6th and 7th Companies are usually composed entirely of Tactical Squads, the 8th Company is comprised of Assault Squads, Assault Centurions and Bike Squads, and the 9th Company is comprised of Devastator Squads and Devastator Centurions. Each of the Reserve Companies maintains its own transports, Dreadnoughts, and additional air and armour assets like Stormtalon gunships, Rhino APCs and Predator tanks. The Reserve Companies normally act in support of the Battle Companies and provide a source of replacements for any casualties suffered by the frontline formations.

The 10th Company of a traditional Space Marine Chapter is the Scout Company composed of Space Marine Neophytes who are being exposed to actual combat for the first time. Those Scout Marines who survive this tour of duty are then welcomed into the Chapter as full Initiates and are granted a suit of Power Armour. They are then moved into one of the Reserve Companies to begin climbing the Chapter's hierarchy -- if they survive.

Post-Ultima Founding Chapter Organisation


Order of Battle of the Ultramarines 2nd Company, "Guardians of the Temple," and the "Avengers of Ultramar," following the arrival of the Primaris Space Marines in Ultramar during the Plague Wars.

As before, the organisation of a Space Marine Chapter in the wake of the Ultima Founding of the Primaris Space Marines comprises 1,000 Battle-Brothers. In comparison to the teeming multitudes of the Emperor's original Space Marine Legions this is few indeed, yet history has proven time and time again that such an elite gathering of martial strength can conquer star systems and even alter the fate of the galaxy itself.

After the resurrection of the Primarch Roboute Guilliman in ca. 999.M41 and his restoration as the ruling Lord Commander of the Imperium, the Codex Astartes was revised for the new era that began with the birth of the Great Rift.

Under the revised organisational scheme for a Space Marine Chapter the updated Codex prescribed, each of the ten companies of a Chapter still boasts one hundred warriors, led by a Captain -- a veteran of countless wars -- and often two Lieutenants as sub-company leaders. A company is still organised into ten squads of ten Space Marines, each led by a Sergeant.

However, the guidelines in Guilliman's updated Codex provide for up to twenty squads of five Battle-Brothers. Furthermore, recent precepts allow for each Battle Company to be reinforced with auxiliary warriors. These additional squads are reassigned from the Reserve Companies.

Of the ten companies, the 1st still consists of the Chapter's most experienced Veterans, and is therefore the most powerful. The Veterans of the 1st Company are still trained to fight in Terminator Armour. It is extremely rare for the Veteran Company to be deployed en masse -- its units normally take to the field alongside the Chapter's Battle Companies.

The revised Codex Astartes decrees that the 2nd, 3rd, 4th and 5th Companies are designated Battle Companies, and generally carry the weight of a Chapter's combat duties. Battle Companies consist of at least six Battleline Squads, two Close Support Squads and two Fire Support Squads. Assault Squads, a type of Close Support Squad, may be deployed as Bike Squads or Land Speeder crews and, just as with their Fire Support brethren known as Devastators, may take to battle as Centurion warsuit pilots. Most Space Marine deployments will consist of a single Battle Company, reinforced by elements of the Veteran, Scout and Reserve Companies as needed.

The Reserve Companies are entirely composed of squads of the same designation. They normally act in support of the Battle Companies and provide a source of replacements for any casualties suffered by the frontline formations. The 6th and 7th Companies are Battleline Companies, each consisting of between ten and twenty of the different types of Battleline Squads. The 6th Company also trains in the use of Assault Bikes and may be deployed entirely as Bike Squads. Similarly, squads of the 7th Company are trained to fight with Land Speeders and Stormtalons, often acting as a light vehicle reserve formation.

The 8th Company is the Close Support Company, and consists of ten to twenty Close Support Squads. It is most often used in an invasion role, or wherever a strong hand-to-hand fighting force is needed.

The 9th Company is the Fire Support Company, consisting of ten to twenty Fire Support Squads. It is the most heavily equipped company in the Chapter, and its heavy cannon-toting Astartes provide unparalleled fire support to their more lightly equipped comrades.

The 10th Company is still made up entirely of Scout Marines -- new recruits whose physical transformation and training is incomplete. The Codex Astartes now dictates no formal size for the 10th Company, as the rate of recruitment is not fixed.

All companies, except the Scout Company, maintain a fleet of Rhino, Razorback and Repulsor armoured transports. The Veteran Company also has a permanent complement of Land Raiders of different patterns and Stormraven gunships for carrying Terminators into the heart of battle. A Chapter's other armoured vehicles form a pool, maintained by the Armoury, that Captains can draw upon. Many companies also include a number of Dreadnoughts, which remain a part of the company in which they served before being interred in the cybernetic sarcophagus.

Every Space Marine Chapter also includes a number of officers and specialists as before, who provide essential battlefield support, spiritual leadership, psychic capability and destructive combat prowess. These individuals are collectively known as the headquarters staff, and include Apothecaries, Chaplains, Librarians, Ancients, and Techmarines.

Over all of these mighty warriors presides the Chapter Master, elevated from the greatest of the Chapter's Captains. He alone is responsible for the deeds of the Chapter, and answers directly to the Administratum. Chapter Masters may select an Honour Guard that are in addition to the company roll, although not all Chapter Masters choose to do so.

Battleline Squads

The most numerous and strategically versatile warriors in a revised Codex-compliant Space Marine Chapter form Battleline Squads. They are flexible enough to press home an attack, or hold a position with withering firepower. Whatever the strategic challenge, the Battleline Squads are equal to the task. The Battleline Squads include:

Close Support Squads

In the revised Codex Astartes, Roboute Guilliman has been very clear about the role and importance of Close Support Squads. A well-coordinated and perfectly timed assault can break the back of any foe, cracking open their lines and sending the remnants of their army fleeing. To make such breakthrough attacks, the designated troops must be fast, aggressive and hard-hitting. The Close Support Squads include:

Fire Support Squads

The Space Marines in a Chapter's Fire Support Squads have a vital role, for they provide heavy covering fire to their Battleline and Close Support brethren. This could be in the form of assassination of prime targets, counter-battery volleys, or the destruction of enemy armour. By their target selection, marksmanship, and the timely application of firepower are countless battles won. The Fire Support Squads include:

Veteran Squads

Of all the fighting formations that make up a Space Marine Chapter, it is the 1st Company that is invariably the most powerful and feared. For a Space Marine to join the prestigious 1st Company is for him to have won renown on battlefields uncounted and to have earned the respect of his Battle-Brothers through deeds of blood and fire.

Most such Veterans have served as Sergeants elsewhere in their Chapter -- sometimes for Terran centuries -- before being accepted into the 1st Company, but a notable few are elevated after performing singular acts of insane heroism. These Space Marines are legends one and all, warriors who have become part of the Chapter's history, and it is every Battle-Brother's ambition to join the ranks of their Chapter's most elite company. The Veteran Squads include:

Scout Squads

Space Marine Scouts chiefly fight as skirmishers, relying on stealth rather than brute force to accomplish missions. Lightly armed and armoured in comparison to their more experienced Battle-Brothers, Scouts operate independently from the main Space Marine force, infiltrating enemy positions and clearing the way for the Chapter's advance.

By operating deep within hostile territory, Scouts reconnoitre the enemy's movements, set ambushes, sabotage supply lines and destroy communications centres in daring commando raids. Sometimes Scouts will pounce unseen to capture enemy commanders for excruciation. The Scouts' goal is to strike hard and vanish before the enemy has the chance to retaliate.

When first inducted into a Space Marine Chapter, a recruit joins the 10th Company as a Scout. He is placed under the tutelage of a Sergeant who will lead him on the field of battle and instruct him in what it truly means to wage war as one of the Adeptus Astartes. Only once he has proven himself worthy of his Chapter by excelling in the ranks of the 10th Company will a Scout be deemed ready to join the main ranks of his Chapter's Battle-Brothers in the Reserve Companies as a full Initiate. The Scout Squads include:

Codex Astartes-Deviant Chapters

Notable Chapters that do not follow the organisational standards of the Codex Astartes include:

These Chapters' unique structures, orders of battle and histories are detailed on their relevant pages.


  • Codex Imperialis, pp. 16-17
  • Codex Adeptus Astartes - Space Marines (8th Edition), pp. 12, 26-27, 68-81, 84
  • Codex: Space Marines (6th Edition), pp. 8-9, 14-15
  • Codex: Space Marines (5th Edition), pp. 13-14
  • Index Astartes I, "Codex Astartes: The Holy Tome of the Space Marines," by Rick Priestley and Andy Chambers, pp. 13-16
  • Warhammer 40,000: Rulebook (6th Edition), pg. 183
  • Know No Fear (Novel) by Dan Abnett