"Emperor knows what pit spawned the hideous apparition we came to know as the Red Terror. It first attacked the outer bastion and twenty-four men died before we drove it away with flamers. We never even found the bodies of Lieutenant Borales and Captain Lowe, just a trail of slime that led away from the command post and into the tunnels. It returned the following night, and the slaughter began anew, but this time we were ready for it...or so we thought."
- — From "Twenty Days in Hell," the retreat from Devlan Primus
The "Red Terror" was a particularly deadly Tyranid Ravener-strain that was a part of Hive Fleet Kraken's invasion of the galaxy, appearing two Terran years before the "official" start of the invasion in 990.M41. Fortunately, this particularly vicious predator was encountered only once by the Imperium as it preyed upon the defenders of the Imperial Mining World of Devlan Primus, located on the Eastern Fringe, over a period of twenty solar days.
It tore into a starport compound to get to its Imperial defenders, killing twenty-four of them before being driven away. Each time it returned, it slaughtered more humans before retreating back into the mining tunnel it had emerged from, devouring the carved-up human remains.
Eventually a search and destroy team was sent into the mining tunnels, only to meet their doom on the dripping scythes of the Red Terror. Though this was the first and last time the Red Terror was ever recorded to have been seen, it is entirely possible that all other encounters with the creature simply yielded no survivors.
Survivors spoke of a beast with a blood-coloured carapace, talons that could tunnel through rockcrete, and a maw so wide it could swallow a human whole. With every re-telling, the legends grew more fearsome and terrifying. Some claimed that the Red Terror was the size of a Ravener; others swore it was as big as a Trygon.
The survivors of the Devlan massacre may well have mistaken the attacks of several such creatures for those of a single beast. However, if the Red Terror is a distinct Tyranid organism, it must be a highly efficient killer; it has never been reported since, but may be because there have been no survivors left to tell the tale.
What became of the Red Terror after the events on Devlan Prime is unknown. One giant ore ship fleeing from Devlan with its cargo of refugees arrived at the world of Adri's Hope ominously dark and silent. No communication was forthcoming from the vessel and it made an automated landing far from habitation.
Those investigating the ship found it to be a blood-drenched abattoir. Men, women and children had been mercilessly butchered in their hundreds, perhaps thousands. Though a breach of quarantine was suspected to have allowed a Tyranid organism to get aboard, nothing was found within the blood-slick vessel.
Whatever the murderous entity was, and what became of it, remained a mystery. Three solar weeks later, Adri's Hope was itself a blood-soaked ruin -- the Beast of Devlan had claimed yet more victims.
It is possible that the Red Terror was an early attempt by the Hive Mind at creating the much larger Mawloc and Trygon bioforms that was released by a Tyranid Norn-Queen to test the new strains' battle efficiency.
Some Imperial scholars have even suggested that this creature was the first Tyranid Ravener, an experiment by the Hive Mind to create a fast-moving killing machine that could appear without warning and consume its prey whole.
- Codex: Tyranids (6th Edition) (Digital Edition), pp. 122-123
- Codex: Tyranids (5th Edition), pp. 22, 37
- Codex: Tyranids (3rd Edition), pp. 32-33