- The First Tyrannic War (745.M41): The Imperium makes first contact with the Tyranid race when Hive Fleet Behemoth invades the Eastern Fringe and annihilates planet Tyran; Behemoth is defeated, though at great cost, by the Ultramarines at the Battle for Macragge.
- The Second Tyrannic War (990-993.M41): Hive Fleet Kraken invades and is, again, narrowly defeated.
- The Third Tyrannic War (997.M41-Present): Hive Fleet Leviathan, the largest Tyranid force yet, invades.
Collectively, the Tyrannic Wars have seen a massive mobilization of Imperial forces and is among the highest prioritized conflicts in the Imperium. Deployed primarily to the Eastern Fringe, casualties among Imperial Guard Regiments have been so high that it seems as if the Tyranids are annihilating them faster than they can be deployed. Over the course of the Tyrannic Wars, many minor races have been rendered extinct and thousands of planets have been reduced to lifeless husks.
Notable Battles of the Tyrannic Wars
- Fall of Tyran
- Battle for Macragge
- Battle of Ichar IV
- Battle of Tarsis Ultra
- Cryptus Campaign
- Devastation of Baal
- 1: Imperial Armour Volume Seven - The Siege of Vraks - Part Three, pgs. 26-27
- 2: The Devastation of Baal (Novel), Chapter Two