>>96383243
HH Book 4, page 50 to 52. During the battle of Port Maw the "Triumph of Reason" was a flagship used to organise a counter attack against traitor forces in the aftermath of a devastating cyber attack.
The sons of Horus board the ship and meme on the mortal crew but then get stonewalled by the Legate Marshal unleashing hundreds of Charonites held in stasis.
For a moment it seems like the ogryn could repel the boarders, then Horus teleports in with the second wave and they slaughter everyone.