Black Reach is an Imperial Hive World located in the Ultima Segmentum that was fought over by the Ultramarines 2nd Company under the command of Captain Cato Sicarius and Goff Klan Orks under the control of the Greenskin Warlord Zanzag following the invasion of Black Reach in 855.M41 by WAAAGH! Zanzag.
In 855.M41, Black Reach, and to a lesser extent, its neighboouring planets Jede'ogh and Voldermach, were overcome by a surging Ork WAAAGH! primarily composed of the Goff Clan under the control of the Greenskin Warlord Zanzag. The planet of Black Reach, though ostensibly valueless, was of great tactical import to the Ultramarines Chapter's Realm of Ultramar. The planet is surrounded by a series of asteroid belts so dense that should Black Reach and its vast array of orbital debris ever become infested by xenos, it would take centuries to exterminate them all.
Furthermore, the magnetic elements of the Black Reach asteroid belt made it extremely difficult to contact Black Reach from out-system, let alone augur the whereabouts of individual armies and their war leaders. An alien invasion of the Imperium could be mustered there, right under the nose of Ultramar, and remain undetected until it was time to strike against the Ultramarines' home region.
All three planets in the Black Reach System were overcome by a surging Ork WAAAGH! which burst into realspace through Jorgund's Eye, a wormhole thought to be connected to the Aeldari Webway in the Vidar Sector. How the primitive Ork fleet pulled off such a feat of interstellar bravado is unknown, but the Greenskin forces descended upon the Black Reach System so quickly that such disturbing questions were put aside by the Ultramarines high command on Macragge in favour of readying for the coming battle.
As an Imperial Hive World, Black Reach's massive hive cities were home to billions of Imperial citizens. Much of the planet's population was slain during the initial assault of WAAAGH! Zanzag, and the hive cities and surrounding territory of Black Reach's northern continent were completely ruined by the sheer intensity of the fighting.
After the defeat of Zanzag by the Imperial forces led by the Ultramarines' 2nd Company and its valiant commander, Captain Cato Sicarius, Black Reach's inhabitants still had to take back the rest of their world from the pockets of surviving Greenskins. One Terminator and twelve Space Marines from the 2nd Company were slain during the Ultramarines' operations on Black Reach.
- Codex: Space Marines (5th Edition), pp. 36-37, 40
- Warhammer 40,000 Rulebook (5th Edition)
- White Dwarf 345 (UK), "The Battle for Black Reach," by Phil Kelly, pp. 52-79