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Battle of Diamat

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Battle of Diamat
Conflict Horus Heresy
Date M31
Location Diamat System
Outcome Strategic Traitor Victory
-Ordinatus Engines seized
Tactical Loyalist victory
-Diamat retaken
Dark Angels Traitors
Primarch Lion El'Jonson
Chaplain Nemiel
Captain Stenius
Magos Archoi (defects)
Several thousand Dark Angels
16 Warships
Tanagran Dragoons
Loyalist Skitarii
Traitor Imperial Army
30 Warships
Sons of Horus Company
At least 6 Warships
light Astartes losses
All killed or fled

The Battle of Diamat was a minor engagement of the Horus Heresy.


When word of the Battle of Isstvan III reached the Dark Angels, the bulk of the Legion was bogged down far from Terra in combat against the Gordian League, something Horus had deliberately engineered. As a result, Lion El'Jonson could only lead a small force of sixteen warships against the Warmaster, deciding to make his first move by going to the Forge World of Diamat and denying the heavy siege engines there to Traitor forces.[1]


When the Dark Angels fleet arrived near Diamat, they were confronted by a larger but second-rate fleet of traitor Imperial Army warships led by several Grand Cruisers. Horus had already dispatched his own forces to Diamat to secure the war engines. After a tense naval battle, the outnumbered Dark Angels prevailed with minimal losses thanks to the tactical abilities of their Primarch. The Dark Angels then landed at Diamat's principle forge-city, sweeping aside what little resistance they encountered. After this the traitors organized a major counterattack, this time led by Sons of Horus Marines. This, compounded with the betrayal of the planet's ruling Tech-Priest Archoi and his Skitarii, made defeat seem imminent for the loyalist forces. The Lion only turned the tide by destroying the primary forges of the planet as they were being overrun, annihilating the traitors and denying Horus their manufacturing ability.[1]


In the aftermath of the battle, the Iron Warriors led by Perturabo arrived over Diamat on their way to Isstvan V to engage in the Drop Site Massacre. Having secretly pledged himself to Horus, Perturabo lied and maintained a facade of loyalty to the Lion. Seeing the siege engines as more useful in Iron Warriors hands, Jonson unwittingly gave them over to the traitorous forces.[1]

See also


Battles of the Horus Heresy
005-006.M31 Battle of Isstvan IIIFirst Battle of ProsperoWar Within the WebwayBattle of the Somnus CitadelUnrest on CalibanSchism of MarsBattle of DiamatDrop Site MassacreBattle of the Rangda SystemFirst Battle of ParamarManachean WarSignus CampaignTreachery at Advex-MorsSiege of CthoniaBattle for Felweather Keep‎
007-008.M31 Battle of PhallBattle of RavendelveRuin of MaerdanBattle of the Alaxxes NebulaPale Stars CampaignBreaking of the Perfect FortressChondax CampaignSecond Battle of ProsperoFirst Siege of Hydra CordatusBattle of the Furious AbyssBattle of CalthBattle of ArmaturaBetrayal at IthracaDeath of CanopusShadow CrusadeCrusade of IronDoom of BorminaDefence of TyrosDefence of the Three PlanetsBattle of UlixisAmbush at EspandorBattle of Aquila AtollBattle of Drooth IIPercepton CampaignBattle of IydrisThramas CrusadeFall of Baztel IIIBattle of VannaheimSecond Battle of ParamarBattle of Constanix IIMezoan CampaignBattle of BodtBattle of DwellErellian SubjugationSiege of Baal
009-010.M31 Battle of MolechBreaking of AnvillusXana IncursionCarnage of MoroxSangraal CampaignBattle of ArissakBattle of PerditusBattle of SothaDrussen AtrocityScouring of Gilden's StarBattle of NyrconBattle of TallarnCataclysm of IronBattle of NocturneWar of DrakesBattle of PlutoSiege of InwitBurning of Ohmn-MatBitter War
011-014.M31 Reaving of the Xibana ReachesLorin Alpha CampaignSubjugation of TyrinthMalagant ConflictBattle of the Kalium GateBattle of CatallusAxandrian IncidentBattle of the Haddon SystemJarrazr IncursionBattle of TralsakTarren SuppressionBalthor Sigma InterventionBattle of AbsolomScouring of the Ollanz ClusterBattle of ZepathSecond Battle of ZaramundBattle of AnuariBattle of PyrrhanSecond Battle of DavinArgolian MassacresBattle of TrisolianBattle of YarantBattle of KradeBattle of DelugeBattle of Heta-GladiusBattle of the Aragna ChainBattle of KallethBattle of the Diavanos SystemBattle of DesperationBattle of Beta-GarmonWar for AgaropsDefence of RyzaBattle of ThagriaPassage of AngelsThassos IncidentBattle of Zhao-ArkhadSerpent's CoilSiege of BarbarusForicaan CampaignBattle of VezdellBurning of VrexorDawn of DesolationDeath of ChemosBattle of Luth TyreYdursk IncidentFall of TenzebarSolar WarRaid on LunaSiege of TerraGreat Scouring