The Astra Militarum, also known as the Imperial Guard in colloquial Low Gothic, is the largest coherent fighting force in the galaxy and serves as the Imperium of Man's primary military force and first line of defence from the myriad threats which endanger the existence of the Human species in the 41st Millennium.
It is comprised of countless billions of men and women -- hundreds of thousands of different regiments, supported by a vast array of light and heavy armoured vehicles that provide the Imperial Guard's primary offensive punch. The Astra Militarum is usually the first Imperial force to respond to a threat if a world's Planetary Defence Force (PDF) fails to suppress it.