Our father slept for one hundred centuries, and while he slept we slept. He was raised from his long sleep, and we emerged into a galaxy far removed from the one we had left behind ten millennia before. We had been destined for the Thirteenth Legion, the Ultramarines, to take part in the Great Scouring, and to resume our father's father's Great Crusade. But we were brought to Mars, early into our trials, after our initial surgeries, and subjected to our long sleep in the care of the Martian Priests. When we were finally woken many of our peers were no longer with us, and had instead been replaced by other aspirants and neophytes. We were taken by full brother Astartes, and trained in our specialisations, and raised to full battle brothers. And then we heard our father's call. We rose to arms, legion, his Unnumbered Sons, and followed him on his Indomitus Crusade.
As Unnumbered Sons we fought, and bled, and died beside our brothers and cousins. And then our father took some of us aside, those who wore the blue of the Ultramarines and bore his gene seed, and he told us we were to be a new Chapter. We would drive through the Cicatrix Maledictum and bring the Emperor's light to the Imperium Nihilus. Brother Captain Elis Rhelian was chosen to be Legatus, first among Captains, our new Chapter Master. He said that we would be Unnumbered Sons no longer, so we took a number—the number of our parent legion; and we became known as the Thirteenth Sons. For our icon we took the chevron of the Unnumbered Sons, black on burnished steel. Our greaves we painted black to represent our new path, striding into darkness. And like a bolt our father fired us at the heart of chaos, and with violence and determination we carved a way through the rift, and so our crusade continues.
The Thirteenth Sons are a Loyalist Space Marine Chapter comprised entirely of Primaris Space Marines, created from the lineage of the Ultramarines and raised during the Ultima Founding of ca. 999.M41.
The Thirteenth Sons are a fleet-based chapter, and their task is to crusade through the Imperium Nihilus, bringing the Emperor's light to dark corners of the galaxy.
In addition to slaying the Emperor's enemies, the Thirteenth Sons diligently seek a method of reconnecting with the hundreds of thousands of worlds cut off from Terra in the galactic north of the Imperium Nihilus.
As a crusading chapter cut off from Holy Terra and without supply lines the Thirteenth Sons rely on captured and scavenged supplies. They have accumulated a large number of relics and trophies for a recently-founded chapter—many senior and veteran battle brothers sport helmets from earlier marks of power armour.
The newly formed chapter fought their way through the Cicatrix Maledictum, their Navigators steering not by the light of the Astronomican, but seeking ripples in the warp that indicated pockets of realspace, hopping from island to island in the tumultuous ocean of the immaterium.
When they finally emerged into true realspace they attempted to take their bearings and ascertain where they had arrived. One of the first signals they detected was a distress beacon from an Imperial vessel identifying itself as the "Light of Prandium", which turned out to be a badly damaged light destroyer of ancient design.
Aboard they discovered a single living being, a first-born Astartes suspended in stasis, wearing a suit of battle-damaged power armour of ancient mark with the colours and symbols of the Ultramarines.
When they were able to rouse him, he identified himself as Sergeant Erginus,
and when he was finally assured that his rescuers were heirs of Guilliman he
insisted that he make his report to one Chapter Master Caspean.
"Caspean? Of what chapter is he master?"
"Verus Caspean? Chapter Master of the Ultramarines Second Chapter!"
"Brother, I know nothing of this Verus Caspean. Marneus Calgar is
the only chapter master of the Ultramarines, and has been for many, many years."
Eventually they determined that, while Erginus had been adrift in the warp for what to him were only a handful of months, a hundred centuries had passed in the world outside, and he was only freed from his perpetual prison when the great rift had torn the glaxay in two, spilling the warp into realspace, and what remained of his vessel had tumbled out like a piece of driftwood. Almost immediately on emerging he had activated the beacon and then entered stasis.
His report of his fleet's losses was far too late to be of any consequence.
As a son of Guilliman, now trapped on the dark side of the rift and ten thousand years from home, Erginus swore into the Thirteenth Sons, and is currently Adjutant to Legate Rhelian.
In a slight deviation from the Codex Astartes, squads of the Thirteenth Sons include a new rank—the Corporal acts as second-in-command to the Sergeant, and takes command of the second combat squad when that deployment strategy is used.
| Title | Codex Equivalent Rank |
|---|---|
| Legate | Chapter Master |
| Aquilifer | Chapter Ancient |
| Optio | Lieutenant (I) |
| Tesserarius | Lieutenant (II) |
| Signifer | Company Ancient |
| 1. | The First |  white trim & helmets | veterans | |
| 2. | Darkstriders |  yellow/gold trim | ||
| 3. | Hidden Shields |  red trim | all battle brothers were recruited as girls | |
| 4. | Bloody Fists |  green trim | extensive experience fighting greenskins | |
| 5. | Shadestalkers |  black trim | ||
| 6. | The Indomitable |  orange trim | battleline reserves | |
| 7. | Shields of Callinon |  purple trim | battleline reserves | |
| 8. | Fire-tails |  grey trim | close support reserves | |
| 9. | Thunderers |  blue trim | fire support reserves | |
| 10. | Pathfinders |  no trim | vanguard marines and scouts |