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Imperial Astartes Legions

When the Emperor first embarked creating the Imperium he created twenty Regiments of enhanced human warriors which would later become the Astarte Legions.
Although twenty Regiments were originally created only eighteen are known of. The remaining two have passed into history, their records, Primarch and name expunged from records for all time. No-one knows their fate and many feel that it is best left that way.

Foreword

The exact organisation of a Legion is an open debate. There are few solid examples of a Legion's example composition and many will argue till blue in the face on the subject but for the purposes of this forum we will assume that the follwoing is accurate based on what is known.
That is not to say that this is the one true official interpretation of the facts only that it is my interpretation based on my knowledge of the subject.
Ultimately this is not intended to be an Index Astartes article but a set of guidelines that will allow players to create credible themed armies using existing Codexes and models.


Organisation
As I have previously stated this is what I see as the most likely representation ideal of a Legion in active service. Based on the Seconding founding it is clear that the Legions varied in size from the likes of the smaller Space Wolves legion to the mighty Ultramarines legion.
Examples of historical documentation varies as you would expect but we can draw some conclusions based on the number of second founding Chapters that each Legion founded following the Heresy and taking into account their casualties at that time.
The following is intended as a model for Legion organisation, although it must be noted that some Legions operated with less than ten companies like the Death Guard who operated with only Seven companies. However, the Space Wolves although having Thirteen companies were reputed to be fewer in number so there is the possibility that company strength varied between Legions.



The Legion
Each Legion is lead by a Primarch commanding ten companies of Astartes, with most Legions concidering the rank of First Company Captain as second in command of the Legion.


Company
Numbering one to ten, each is led by a Captain and seconded by the First Sergeant. Each Company consists of one thousand Astartes divided into one hundred squads. Each Squad is led by a Sergeant who reports directly to the First Sergeant.



Creating the Legion

I'm using the following list that I created for representing the equipment available for the era. There are probably things people will disagree with but it's the simplest way of making the army just using Codex: Space Marines.
Traits can be used to define the characteristics of your chosen Legion in anyway you see fit.
It's best to avoid Chapter specific Codexes like Blood Angels as they weren't affected by the Thirst or Black Rage untill after Sanguinus's death at the hands of Horus. Again, this is a matter of personal choice and interpretation. It's your army at the end of the day.

The following vehicles/units are excluded from the Codex:
Librarians, Landraider Crusaders, Razorbacks and Predator Anihilators.

The following weapons are excluded from the Codex:
Plasma Cannons/Multi-meltas in Tactical, Devastator, Command, Reclusiam Command and Veteran squads.


The following Wargear is used as "counts as"

Oath of Moment: Counts as Purity Seals

Reaper Cannon: Counts as Assault Cannon when used in Terminator squads. Only one to be included in each squad.

Battle Standard: Counts as sacred standard.

Combi-bolter: Counts as Storm Bolter.

Jet Bikes: Counts as Bike Squadron.

Assault Squads 0-1 : Player discretion advised here though. It is said that the jump packs were few in number at the time of the Heresy/Great Crusade (see "The Raptor Cult" article published in WD) in the same way that Terminator squads are few in number today. Jump pack troops were supposed to only be used in specialised missions and it was seen to be a mark of honour to be in such a squad.


Other Options

The logic behind Multi-Meltas and the Salamanders.
Many argue that the Salamanders should have access to Mulit-Meltas as it is often seen as a defining characteristic of the Chapter.
Unfortunately this last statement is the flaw in the arguement. The reason contemporary Salamanders Chapter use the Mulit-Melta is because is is available today in it's man portable format. However, at the time of the Heresy it is suggested that it was only mounted on vehicles and Dreadnoughts.
During the creation of Codex Chaos a number of weapons were omitted from the Codex to create a distinct archaic feel to the army. This resulted in the Traitors replacing the Stormbolter with the Combi-bolter, the Assault Cannon with the Reaper Autocannon and the total lack of Plasma Cannon and Multi-Meltas.
However, having said that at the end of the day it is your army and if you want to include Multi-Melta and Plasma Cannon please do not let anyone tell you otherwise.

Chaplains
They were present up untill the Heresy itself when many of the Traitor Legions killed the Chaplains of their own Legion. Obviously Legions like the Word Bearers weren't party to this and kept their Chaplains as spiritual leaders.
Notable Chaplains of the Time include Charmosian of the Emperor's Children, Xavier of the Salamanders and Annellus of the Blood Angels.


Alternative Formations and Units.

It is most likely that the modern Chapter is based on the formation known as the Spear Tip.
The Spear Tip is a surgical strike formation at company level that is designed to strike at the heart of an enemy using drop pods and the fore-runner to the Thunder Hawk dropship known as a Stormbird.
The Storm Bird was conciderbly larger than a Thunder Hawk with a larger amount of weaponary mounted on the craft, capable of deploying troops onto a planet's surface.
In keeping with this theme Spear Tip formations should best represented using Drop Pod armies.

Recon Squads
In addition to the Scout squads that were made up of Neophytes it appears that Recon squads were employed by Legions made up of fully armoured members of the Astartes (Horus Heresy Artwork Books). Although there appears to be no other mention of them in any of the literature.
These are best represented using the Veterans Squad with the Infiltrate ability.

Why No Librarians?
According to the decree of the Council of Nikaea made when the Emperor bought Magnus to trial for his continued use of sorcery it was declared that the Legion Librariums would be discontinued. Those brothers who were psykers were returned to their companies.
Having said this the Thousand Sons refused to bow down to the order and continued to practice their arts. Therefore Thousand Son armies should be allowed to use them.

Why No Land Raider Crusaders/Razorbacks/Predator Annihilators?
All of these were either created or rediscovered after the Heresy. Crusaders were created by the Black Templars, Annihilators were created by the Space Wolves and the Razorback was resicovered as a lost STC design.

Why No Primarchs?
Whilst Primarchs can be represented with house rules these forums are about using existing codexes to create playable gaming legal armies. Therefore I have decided to leave them out of the suggested lists.


Land Speeders
The Land Speeder saw action in both the Legions and the Imperial army before and during the Heresy. The reason some think that it wasn't present is due to the confusion caused by the Chaos Codex. Although they had them at the time of the Hersy they do not have them now because they were difficult to maintain.

Armour Variants Guidelines.
Again this is down to the individual modelling their army and like all of the suggestions here is concidered a guideline.
The Legions were in the process of being equiped with the MkIV armour when the Heresy broke out but was quickly replaced with the MkV armour as the Tech marines, being inexperienced with the new armour design, were finding it difficult to replace or even reproduce MkIV parts. This led to the development of the MkV which exclusively used parts from the earlier marks of armour as opposed to the more exotic MkIV parts.
The MkV was a temporary stop gap for the MkVI which was being designed at roughly the same time as the MkV. The Loyalists had access to the MkVI armour first but as the Traitors overran the production facilities they too began to produce the Corvus suits.
The Aquila or Imperator MkVII didn't become available untill the final days of the Siege of Terra.

Armour variants availability were historically as follows:

MkI Thunder Pattern Armour - Wars of Unification (Early Pre-Heresy)

MkII Crusade Pattern Armour - Conquest of the Terran System (Early Pre-Heresy)

MkIII Iron Pattern Armour - The Great Crusade (Pre-Heresy)

MkIV Maximus Pattern Armour - The Great Crusade/Heresy (Late Pre-heresy/early Heresy)

MkV Heresy Pattern Armour - Horus Heresy (Heresy Era)

MkVI Corvus Pattern Armour - Horus Heresy (Mid Heresy)

MkVII Aquila/Imperator Pattern Armour - Siege of Terra (Late Heresy)

MkVIII Errant Pattern Armour - Post Heresy