The Fist of Iron was an ancient Gloriana-class Battleship that served as the flagship of Ferrus Manus, the Primarch of the Iron Hands Legion during the Great Crusade and the Horus Heresy of the late 30th and early 31st Millennia. This flagship led the flotilla of Iron Hands warships which comprised the X Legion's 52nd Expeditionary Fleet. The massive vessel drifted in the void like a slab of steel and bronze, its hull scarred and unpainted from the damage it had sustained during many campaigns of Imperial Compliance. Like their Primarch, the Iron Hands cared little for ostentation or the embellishment of the vessels within their Legion fleet.
During the opening days of the Horus Heresy, it was within the Iron Forge of the Fist of Iron that Fulgrim, Primarch of the Emperor's Children Legion, attempted to sway his brother and great friend Ferrus Manus to the Warmaster Horus' cause of rebellion against the Emperor and his Imperium. Fulgrim had sent the bulk of his III Legion and the 28th Expeditionary Fleet on to meet Horus and the 63rd Expeditionary Fleet in the Istvaan System while he and a small force aided the Iron Hands' 52nd Expeditionary Fleet in retaking the world of Callinedes IV from the Orks. Great bonds of friendship and brotherhood had long existed between the III and X Legions, and Fulgrim felt that he could convince Ferrus of the righteousness of Horus' cause. Fulgrim's hope proved disastrously wrong and the meeting of the two Primarchs in Ferrus' private inner sanctum did not go well, as Ferrus was utterly outraged that his brothers would dare to turn against their father the Emperor. The meeting ended in violence, as the Gorgon made his difference of opinion over continued loyalty to the Emperor known to the Phoenician with his weapons, determined to stop Fulgrim's betrayal of the Imperium before it could begin. Ferrus attempted to use his silvery necrodermis hands to destroy Fulgrim's golden sword Fireblade, but the resulting explosion knocked him unconscious.
Fulgrim intended to kill his unconscious brother with the weapon he had forged for him, the warhammer Forgebreaker, but proved unable to kill his oldest friend despite the promptings of the Slaaneshi daemon embedded within the Silver Sword of the Laer that now corrupted his soul. Instead he took the wonderous weapon that he had once crafted in brotherhood for Ferrus as a reminder of their former friendship, and left behind Fireblade, which Ferrus had forged for him. When Fulgrim emerged from Ferrus' inner sanctum, he gave a signal to his elite Phoenix Guard, who instantly beheaded all of the Iron Hands Morlock Terminators who served as Ferrus' own elite bodyguard with their Power Halberds. The Emperor's Children also nearly slew the Iron Hands' First Captain Gabriel Santor. Fulgrim successfully fled the Iron Hands' expeditionary fleet in his personal assault craft, the Firebird, as he ordered his warships, the Battle Barge Pride of the Emperor and its Escorts, to open fire upon the ships of the 52nd Expeditionary Fleet. Fulgrim called a halt to the attack before the destruction of the Fist of Iron was complete. Leaving the crippled X Legion's fleet becalmed, the ships of the Emperor's Children disengaged and made the translation into the Immaterium to rendezvous with the rest of the 28th Expeditionary Fleet and the forces of Horus in the Istvaan System.
The ultimate fate of the Fist of Iron following the events of the Horus Heresy is unknown.
One of the primary chambers within the Fist of Iron was known as the Anvilarium, which served as a reception hall for any business to be conducted between Ferrus Manus and outsiders. This vast chamber resembled a mighty forge with huge, hissing pistons rising and falling at the edges of the audience chamber, and the distant clang of hammers echoed through the sheet metal of the floor. It was a cavernous space, with the pungent aromas of oil and hot metal heavy in the air, the space redolent of industry and machines. Within the Anvilarium, mighty deeds were planned and unbreakable bonds of brotherhood were forged. The elite Iron Hands honour guard of Morlocks Terminators stood sentinel around the edge of the chamber, the mightiest of them protecting the gates of the Primarch’s inner sanctum, known as the Iron Forge. The Terminators' towering forms were rendered ghostly by the hissing clouds of steam that billowed from the deck, the fearsome visage of the Morlocks making them look like the vengeful predators that howled across the frozen tundra of the Iron Hands' homeworld of Medusa, for which they had been named.
Ferrus Manus' chambers aboard the Fist of Iron, known as the Iron Forge, were constructed of stone and glass, as cold and austere as the frozen tundra of Medusa. Those lucky enough to be invited within could almost feel the chill of the Iron Hands' icy homeworld in the design. Blocks of shimmering obsidian carved from the sides of undersea volcanoes kept the chamber dark, and glass cabinets of war trophies and weapons stood as silent sentinels over the Primarch’s most private moments. The Iron Forge was were Ferrus Manus kept his most prized relics and personal creations. Its gleaming walls were fashioned from smooth, glassy basalt and hung with all manner of wondrous weapons, armour and machinery crafted by the Primarch’s silver hands. A vast anvil of iron and gold sat in the centre of the forge, and Ferrus Manus had long declared that none save his brother Primarchs were permitted to enter this most private sanctum. Vulkan of the Salamanders Legion had once declared it a magical place, using the language of the ancients to describe the magnificence it contained. To honour Ferrus’ skill at the forge, Vulkan had presented him with a Firedrake banner, which hung next to a wondrously crafted gun with a top loading magazine and perforated barrel formed in the shape of a snarling dragon. Its brass and silver body comprised the finest workmanship ever seen, its lines and curves so beautiful that to simply label it a weapon was to deny that it was in fact a work of art.
- Fulgrim (Novel) by Graham McNeill, pp. 94, 96, 154-155, 158, 163, 172, 179, 300-301, 304-305, 316, 335, 369, 396