Suicide cult: the Sago dreadnoughts
To kill an Astartes is not easy. Even so far as to render critical wounds nonfatal, the Astartes physique can withstand punishment, poison and pain enough to drown a whole city in death. What does it take to kill a Sago marine enough to permit interrment into the sacred sarcophagi, which is the pinnacle of every joy and terror to him?
Ah indeed, why would so hatefully storied a Chapter call their fleet of dreadnoughts so simple a term? Surely you can divine why.
If the Quicks of the Sagodjur Fjorlag are permitted one secret they alone might keep, it is the number of dreadnought sarcophagi hidden away in the storage pits and the battle-units to be possessed thereby. When a new Quick is sent to Mars for his full decade of primary industry and apprenticeship, the greater part of his focus is put to the enigmae of the dreadnought chassis and its divers forms. For in the particular strategio best loved by the sadistic Sago, dreadnoughts are the heavy armour to which every commander falls back upon.
As stanchions sunk into the tide of sewage they stand steadfast in the maelstrom of war, beacons by which the wavering sanity of their living brothers might force back the Darkness and fight on.
The Sago Astartes have claimed (all lies) to possess every pattern of dreadnought the galaxy might contain. This in itself is a rather groundless claim, but what they can lay claim to is possession of the rarest.
Over their long history they have been called the Beacons Unto Him, the Cross-eyed and the family of the Tweedles amongst many other epitapths as long and incomprehensible as the Nastrondite tongue could contrive. Without a doubt these hulking, scorn-blasted masses of ceramite and silence are the absolute rarest pattern of dreadnought ever wreaked upon an unwanting Imperium. Few know of their existence and fewer are given that supreme grief upon griefs to be interred therein, for the purpose of an Amphis' Bane is as strictly unique as it is unecessary; for the only Astartes allowed to be therein interred were twin brothers in life.
When the Alpha legion had cemented their place in the murky gaps between their brother legions, it has been committed to the most unreliable of record that, in order to either gladden the hearts or shut the mouths of their cousins, Alpharius commissioned the making and distribution of many beautiful gifts which he personally - for all the worth that gesture might have, given his status - gave to his brother primarchs to bolster the legions and serve upon the manifold fronts of the Emperor's Great Crusade. As but a few examples, to the children of the IIXth, XIVth and XIIIth he gave special call-signs, phrases when spoken into any radio device could be heard from anywhere across the layers of existence by their father-progenitors, and thus unite one to the other: to the IIIrd he sanctioned the giving of nine feathers of a mercury derivative that could unlock any door: and to the VIIth, he gave Amphis' Bane pattern dreadnoughts.
How the Sago Astartes came to have every single recorded Amphis' Bane unit is a complete accident, probably stemming from the same circumstances that led to their their interrment upon Nastrond. So specific was the requirements of these machines that perhaps the Preatorian chose to store them away with the intention of returning for them when need drove him thus. And now every single one of these units have been activated and utilized. All at once.