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A Traitor Iron Warriors Terminator being burned alive by Phosphex during the Battle of Tallarn.

Phosphex Weapons were deadly incendiaries which usually take the form of a bomb or artillery shell containing a corrosive toxic and flammable compound that is nearly impossible to extinguish short of exposure to the void. They were used at times by the Imperial military forces of the Great Crusade and Horus Heresy eras in the late 30th and early 31st Millennia.

Thankfully these rare and deadly armaments, now known as Phosphor Weapons, are used very sparingly within the arsenals of the Imperium of Man's military forces in the 41st Millennium, as only a limited and irreplaceable stock remains deployed among the Skitarii of the Adeptus Mechanicus and the siege armies of the Astra Militarum.


Phosphex is a rare, corrosive and toxic incendiary compound utterly inimical to life, originally deployed by the Imperial armed forces either in the form of large canister bombs or heavy artillery shells. It expands on contact with air into a seething liquid mist which burns with an eerie white-green flame that is attracted to movement. This gelid flame ignites metal and eats relentlessly into living tissue, and cannot be extinguished short of exposure to vacuum. As effective as this horrific weapon is, its use is not widespread as it has a tainting effect beyond even Rad Weapons on the environments in which it was employed. It remained within the arsenals of the Space Marine Legions during the time of the Great Crusade and Horus Heresy as a weapon of dire resort.

In 009.M40, the rogue Tech-priest Veriliad, after leading his Skitarii to a stomach-churning victory during the Cremation of Alcadia Secundus, destroyed the Adeptus Mechanicus' ability to make Phosphex Weaponry. Having seen the crawling horror of the living, white-green flame, Veriliad destroyed the lone STC database still in existence for the substance's creation. Efforts to recreate it have been unsuccessful ever since. Decried as Heretic Technis by the rest of his order, Veriliad was tied to a stake and shot with the pistol known as Phosphoenix, the finest such weapon ever produced. Perhaps fittingly, he was burnt alive by the very living flame he had tried to extinguish.

Notable Phosphex Users

  • Death Guard - It is of note that the Death Guard Legion under Primarch Mortarion quickly became associated with the use of alchemical and radiation weaponry to a greater extent than any other Astartes Legion, further darkening their reputation with their Battle-Brothers. Simply put, the use of toxic gas, crawl-burning Phosphex and contaminated rad-shells did not rankle their Legion's honour as it did for some, while Mortarion himself was a master of such weapons and student of the most horrific arts of war and had no compunction in their use against any enemy that threatened humanity.
  • Iron Warriors - The elite artillery formation of the ancient Iron Warriors Legion, known as the Stor-Bezashk, was renowned for its consummate skills in siege warfare and had a reputation as a master of destruction. The siegemasters of the Stor-Bezashk had command of weapons and war engines unseen outside of the ranks of the Mechanicum's Ordo Reductor, and had direct battlefield command of the Legion's extensive stockpiles of atomic shells, Phosphex reserves and rare gravitic munitions.
  • Word Bearers - In accordance with their practice of shaping a new religion around the worship of the God-Emperor, and later their determination to spread the worship of the Dark Gods, the Word Bearers deployed a unique formation of Destroyers known as the Ashen Circle. Equipped with Jump Packs to hasten the process, they would scour the worlds invaded by the Legion for monuments, leaders, books, and other significant cultural and religious icons that were deemed heretical to the teachings of Lorgar and destroy them with Flamers and Phosphex Weapons. Unlike many Astartes Legions who either distrusted or held little regard for those units equipped with Phosphex, the Ashen Circle was seen as an elite honour company for the most devout and skilled of the XVII Legion, with at least one individual, Zardu Layak, being promoted to command of a Word Bearers Chapter and many others to service as Chaplains.

Phosphex Weapon Types

See Also


  • Codex: Adeptus Mechanicus - Skitarii (7th Edition), pg. 179
  • The Horus Heresy - Book One: Betrayal by Alan Bligh, pg. 231
  • The Horus Heresy - Book Two: Massacre by Alan Bligh, pp. 142, 257
  • The Horus Heresy - Book Three: Extermination by Alan Bligh, pg. 112
  • The Horus Heresy - Book Five: Tempest by Alan Bligh, pp. 105, 111, 247