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Warhammer 40K: Adeptus Astartes Firstborn & Unnumbered Sons

4 Minute Read
May 21 2021

Today  we look at two generations of Adeptus Astartes and the shared but uncertain path both walk in defense of the Imperium.


Firstborn is the Imperial term for original template pre-Primaris Space Marines.

For ten thousand years from the Great Crusade until the end of the Thirteenth Black Crusade, the Firstborn were simply the Adeptus Astartes. However following the development of Primaris Space Marines by Belisarius Cawl the “Firstborn” as they became known faced the prospect of obsolescence at these larger, physically stronger, and mass produced warriors. Originally in the early stages of the Indomitus Crusade most Primaris were produced by Cawl himself and though developed by the Gene-Seed of the Primarch‘s lacked a distinct identity, instead being gathered in armies known as the Unnumbered Sons. However as the Crusade progressed the Unnumbered Sons were distributed to either new Chapter‘s of the Ultima Founding or into existing Space Marine Chapters.

Even though 94% of Chapters have accepted Primaris Marines into their ranks Firstborn-Primaris relations have had issues. To many, the Primaris were new arrivals often recruited away from a Chapter’s homeworld and new to the culture, traditions, and ways of the Chapter. Many arrivals from the Unnumbered Sons into existing Chapters felt like strangers. When some Firstborn first saw the Primaris, they regarded them as mutants. This tension was exemplified in the Space Wolves, where many Wolf Lords resisted accepting Primaris Space Marines.

In the White Scars, many Firstborn saw that these warriors were not of Chogoris nor knew the ways of their Chapter’s culture, but at the same time understood the necessity of Primaris Marines in defending the Imperium. Notable Space Marine officers who have openly expressed distrust of Primaris Space Marines are Flesh Tearers Chapter Master Gabriel Seth and Raven Guard 9th Company Captain Vos DelornIn the Unforgiven, there was much hesitancy over allowing Primaris Marines into the Inner Circle.

In an attempt and promote unity between Firstborn and Primaris Marines, Roboute Guilliman often used them as political equerries and symbols of his authority. For their part, most Primaris Marines looked to their Firstborn brethren for sage advice, drawing from experiences from their many centuries of conflict. Primaris Marines learned this lesson in the early days of the Indomitus Crusade, where many had fallen in battle due to their lack of experience.


Originally, Firstborn could not survive being converted into Primaris Marines. However this changed when Ultramarines Chapter Master Marneus Calgar crossed the Rubicon Primaris and became the first Firstborn to survive transitioning into a Primaris Space Marine. Since then, the process has been repeated for Firstborn across multiple Chapters.

Unnumbered Sons

The Unnumbered Sons was a classification of Primaris Space Marine that was created by Lord Commander Guilliman during the formation of the Indomitus Crusade. They were officially known as the Unnumbered Sons of the Primarchs, but some within their ranks referred to themselves as Greyshields.

Of the many thousands of Primaris Space Marines created by Archmagos Dominus Cawl, half were formed into new Chapters, from the so called Ultima Founding, while the rest were gathered into nine Legion sized armies. These armies were descended from the nine loyalist gene-lines, who wore the livery of their founding Primarchs, and were then further organised into Chapter-sized formations. These armies were then made to fight in mixed gene-line squads, by Lord Commander Guilliman, who hoped the different gene-lines would learn from each other and not repeat the misunderstandings that have occurred between Chapters in the past. Despite fighting in mixed units, the Unnumbered Sons were united by their prominent badges that were crossed with pale grey chevrons.

The Unnumbered Sons were a major force within the Indomitus Crusade, but as the Crusade progressed their strength dwindled; both from battle losses, as well as being separated from their groups on the orders of Lord Commander Guilliman. Those Primaris Space Marines that were separated from the Unnumbered Sons, were usually assigned by companies, squadrons and even smaller numbers, to understrength Chapters encountered by the Indomitus Crusade. However, sometimes Guilliman created whole new Chapters where they were needed, such as when important worlds needed to be defended from the Imperium‘s enemies. Sons of Guilliman could become Aurora Marines, Doom Eagles, etc., Sons of Dorn could become Black Templars, Imperial Fists, etc. and so on.

However, by the time of the Battle of Raukos, only twenty thousand of the Unnumbered Sons remained within the Crusade. This proved to be the last battle the Unnumbered Sons would fight in though, as Lord Commander Guilliman officially ended the Indomitus Crusade and ordered the disbandment of the group. Some of the Unnumbered Sons were then formed into new Chapters, such as the Knights Cerulean, Praetors of Ultramar and the Wolfspear; while most would take the lessons they had learned from each other, to established Chapters descended from their Primarchs.


~ We give thanks to Emperor for his Angels of Death, both old and new.


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