|Chapter Master||Godfrey Magnusson (presumed)|
|Strength||Unknown, but a lot smaller than most chapters|
|Specialty||Secrecy, being Inquisitional henchmen|
|Colours||Dark blue with black trim, helmet stripe, and chest|
The Stormwatchers are a secret Space Marine Chapter that serves the Inquisitors of the Caligari Sector, invented for the video game Warhammer 40,000: Inquisitor - Martyr. At some point a bunch of them fell to Khorne and massacred most of the loyal ones, with the survivors hiding their existence to ensure they didn't start rampaging around the Caligari Sector to locate them. They eventually found out though.
Their Primarch has not been revealed so far, though he can't be Rogal Dorn, because in the game Inquisitor: Martyr, a Stormwatcher named Caius Thorn goes into suspended animation to survive his lethal injuries, which is something the Imperial Fists cannot do since their Sus-an Membrane does not function. He could be Ferrus Manus, because Caius seems to share the Iron Hands' unreasonable contempt for weakness. There's a point in Inquisitor: Martyr where he rebukes a cardinal for luring the Inquisitor into a Dark Eldar trap, even though said cardinal was coerced by torture and managed to sneak a subtle warning in his communications. The cardinal was not strong enough to resist the coercion altogether, and that made him a failure in Caius' eyes.
- Grand Master Godfrey Magnusson: The leader of Stormwatchers at Ascalon after it came under attack by the Voidrippers, the fallen Stormwatchers.
- Sergeant Caius Thorn: Leader of the squad that accompanied Inquisitor Klosterheim aboard The Martyr, where he lost his squadmates and got his arm and leg torn off by a Helbrute. He got better though and joined the main character Inquisitor's group.