The Imperial Army was the largest military force of the early Imperium, raised during the Great Crusade to support the Space Marine Legions. It garrisoned worlds, fought sieges, and waged mass invasions across the galaxy, but its subordination to the Legions led to its near-destruction in the Horus Heresy.
What was the Imperial Army?
Also called the Imperialis Auxilia, it was the Imperium’s primary human military, founded during the early Great Crusade. It filled the need for more manpower to support the Astartes Legions, quickly taking on garrison duty, sieges, and mass invasions.
It was part of the Excertus Imperialis and was subordinate to the Astartes command structure. Its fleet branch was the Imperialis Armada, and its aerial warfare branch was the Divisio Aeronautica.
- Founded: during the early Great Crusade, from Unification Wars-era units
- Dissolved: after the Horus Heresy
- HQ: Terra, led by the Lord Commander Militant
- Sub-branches: Solar Auxilia, Imperialis Militia, Imperialis Armada, Divisio Aeronautica
Origins and history
The first units came from Strife-era formations on Terra that the Emperor allowed to keep serving after the Unification Wars. These became the Old Hundred, the initial core of human soldiery at the start of the Great Crusade.
As the Emperor conquered worlds, he expected their populations to maintain defences against rebellion and invasion, much like later Planetary Defence Forces. From these local forces, the Imperial Army took shape. Initially used as garrisons, they were quickly pushed to the forefront of the Crusade.
Organisation and strength
The Army’s fighting elite was the Solar Auxilia, making up roughly 20 to 25 percent of its strength by the end of the Great Crusade. The full force numbered in the many billions or even trillions, and it also maintained auxiliaries known as the Imperialis Militia.
Regiments were the basic building blocks, and the Imperialis Armada handled fleet operations. The Covenant Militarum was another element of its structure.
| Component | Role |
|---|---|
| Solar Auxilia | Elite fighting force, 20-25% of Army strength |
| Imperialis Militia | Auxiliary forces |
| Imperialis Armada | Fleet subset, subordinate to the Army |
| Divisio Aeronautica | Aerial warfare branch |
The Horus Heresy and dissolution
Because the Imperial Army was subordinate to the Astartes Legions, it tore itself apart when half the Legions rebelled. Thousands of Army commanders carved out their own empires, loyal to neither Horus nor the Emperor, and it took centuries for the Imperium to recover.
After the Heresy, the armed forces were restructured to prevent any one person from holding that much power again. The Imperial Army was dissolved, its place eventually taken by the Astra Militarum and other organisations.
Key facts
- The Imperial Army was also known as the Imperialis Auxilia.
- It was founded during the early Great Crusade and dissolved after the Horus Heresy.
- Its elite troops were the Solar Auxilia, about 20-25% of its strength.
- The Imperialis Armada was its fleet branch, and the Divisio Aeronautica handled aerial warfare.
- It was subordinate to the Astartes Legions, which led to its fragmentation during the Heresy.
FAQ
What was the Imperial Army in Warhammer 40k?
It was the Imperium’s main human military during the Great Crusade, also called the Imperialis Auxilia. It supported the Space Marine Legions and handled garrison, siege, and invasion duties.
What happened to the Imperial Army after the Horus Heresy?
It was dissolved as part of a major restructure. Its regiments were split up and reorganised into what later became the Astra Militarum, to stop any single commander from wielding so much power again.
What was the Solar Auxilia?
The Solar Auxilia were the elite troops of the Imperial Army, making up about a fifth to a quarter of its strength by the end of the Great Crusade. They were better equipped and trained than standard Army regiments.