The Solar Watch, known also as the "Castellans of the Blessed Worlds," is a Shield Host of the Adeptus Custodes, the stalwart guardians of the Emperor of Mankind. The Sol System is amongst the most heavily fortified of Mankind's stellar holdings. The Adeptus Custodes consider its worlds, star forts and space lanes to be extensions of their master's palace, and ensure they are guarded accordingly. Therefore, it has fallen to the Custodians of the Solar Watch to act as castellans -- standing eternal vigil for threats against the Throneworld and the worlds of the Segmentum Solar.
From the vast orbital fortresses of Luna to the cloud-keeps of Jupiter and the deep-space star forts of the Halo Belt, Humanity maintains hundreds of strongholds throughout the Sol System. Billions of weapons point menacingly into the dark gulfs of space, ready to unleash spectacular devastation upon any foolish enough to threaten Mankind's seat of power. Armoured towers and gargoyle-festooned bastions loom over every approach, sanctified against the foul machinations of the Emperor's many foes. Entire fleets of Imperial Navy ships prowl the space lanes, vigilant for the slightest threat. Yet perhaps the most formidable of all Terra's outer defensive measures are the Custodians of the Solar Watch.
Consisting of several Shield Companies of varying strength, the Solar Watch swear binding oaths to keep guard over the outer bastions of the Throneworld. They see themselves as the first true line of defence for the Imperial Palace, and believe that it is their duty to ensure that no external threat ever makes it as far as Terra. To this end, they constantly patrol routes between the worlds and void structures of the Sol System, ever vigilant for danger.
Though they typically travel via naval craft and intrastellar trade ships, the Solar Watch maintain a formidable concentration of Venerable Land Raiders, and are typically able to deploy forces that are predominately, if not entirely, mechanised. This allows them to respond swiftly, and with overwhelming force, to any potentially threatening situation that may develop. While such dangers are not common within the Sol System, they are certainly not unheard of; the Solar Watch have been instrumental in bringing an end to daemon-worshipping Chaos Cults, Inquisitorial coups and subtle xenos incursions on every world bar Mars. While their authority technically extends to the Red Planet, the Adeptus Custodes are wise enough to maintain cordial relations with the servants of the Omnissiah, and so travel to that world only occasionally, trusting the Cult Mechanicus to police its own deviants.
The more aggressive of the Captain-Generals of the Adeptus Custodes have traditionally charged the Solar Watch with performing sporadic Talon Sorties. These involve the Watch gathering Shield-Company-strength forces and launching strikes against prevailing threats in the star systems closest to Terra. The Solar Watch do not waste their resources in war zones already heavily invested in by Imperial forces. Rather, they sally out to destroy developing threats or eliminate enemies that have broken existing Imperial lines. Deploying aboard their Venerable Land Raiders, they slam into their enemies in fast-moving armoured spearheads. Prioritising the slaughter of command elements and heavy combat assets, the Solar Watch cripple their enemies' capacity to function as an army of conquest before abruptly withdrawing, leaving lesser Imperial forces to mop up what remains. After all, the duty of guarding the Sol System is a vital one, and the Solar Watch cannot leave their posts for long.
- Zagstomp's Doom (ca. Unknown Date.M42) - The Orks of WAAAGH! Zagstomp overrun the Iron Warriors Citadel of Miseries after a gruelling three-year siege. Grown massive and powerful on a diet of constant warfare, and equipped with the looted tanks and war engines of the butchered Iron Warriors, Zagstomp's hordes board their ramshackle voidships. Before they can attempt to punch their way into the Warp, Custodians of the Solar Watch materialise within the engine decks and mek bays of the Greenskins' capital ships. Guns blazing, the Custodians hold off the Orks long enough to plant vortex implosion detonators on every ship. The survivors then teleport back to their own ships and jump away into the Warp. In attempting to give chase, the Orks trigger the Vortex bombs, and their vast fleet -- which Imperial doomscryers warned would appear on the fringes of the Sol System if left unchecked -- is consumed by the ferocious energy storm that follows.
- Codex: Adeptus Custodes (8th Edition), pp. 26, 33, 48