Reunited wth their primarch, Perturado, the Iron Warriors soon gained the reputation of being brutal and merciless during the seige!
Via our good friends at Lexicanum
Even before being reunited with their primarch, Perturabo, the Iron Warriors were known for an affinity with technology and the clinical application of logic to military problems. This affinity was channeled by Perturabo, a skilled practitioner of siegecraft, into the mastery of that form of warfare. These abilities were increased by cross-training with the Adeptus Mechanicus. Their Warsmiths could match skills with Magi and it is said that Perturabo could beat any and all in the art of machine engineering. Their methodical attitude made them merciless men in battle and siege. After the siege works were built there was a choice given to the besiegers; either they throw down their arms then and there or the Iron Warriors would show no mercy. Just like many other legions they soon gained the reputation of brutality during siege, not to mention their merciless manner after the siege took place. A number of warrior societies within the Legion also existed during this time, most notably the Dodekatheon, Apolakron, Kheledakos, and Lyssatra. It also maintained a special unit known as the Stor-Bezashk, which commanded mighty siege weapons unseen outside of the Adeptus Mechanicus‘ Ordo Reductor itself.
The Iron Warriors suffered a great deal of dispersion during the Great Crusade, with various units being detached for separate siege and garrison missions.
The strategic command of the Legion were overseen by Grand Battalions, which functioned similarly to a Chapter, but had a larger stockpile of armor, artillery, and logistical support than other legions. The Iron Warriors had a notably high rate of attrition, so the strength of the Grand Battalions fluctuated. Some had as little as 500 Legionaries and others had an excess of 4,000. Severely depleted Grand Battalions were folded into active units. Grand Battalions were commonly divided in Cohorts or Grand Companies. Below these were Line Companies and Armor Centuries. The companies roughly had 100 Legionaries and the centuries had a range of 20 to 50 armor units. In each Grand Battalion there were elements of the Tyranthikos, informally known as the Dominators. These were the Legion’s Terminator veterans.
Tactically, Iron Warriors were organised as a number of Grand Companies each commanded by a Warsmith. Originally each Grand Company would have had a similar organisation, totaling around 1,000 Space Marines. At the time of the Heresy, the Legion had at least twelve Companies, although with the widespread deployment of many small detachments of the Legion at the time it is impossible to be sure if this figure of around 12,000 fighting Astartes was their maximum strength. The overall size of the Legion was between 150,000 and 180,000 Marines.
