The Astra Militarum make up the bulk of the armies of the Imperium of Man in Warhammer 40k.
Being regular humans recruited from thousands of Imperial worlds across the galaxy, it's a hard life being in the Guard. The Astra Militarum are treated as expendable by generals, and will happily overrun enemies using the weight of numbers at their disposal, regardless of the cost of lives.
Serving in the Imperial Guard is one of the highest honours a human can achieve in the 41st millennium however, and many regiments are fiercely proud of their history - from the jungle fighters of the deathworld Catachan, to the icy warriors of the Valhallan regiment.
A variety of tanks are at the disposal of the Astra Militarum, and some armies fight using entire tank companies as their preference.
The Astra Militarum gives you a great opportunity to create a regiment in your own colour scheme and with its own backstory, after all, who doesn't love an underdog?