Though the towering AT-AT proves mostly invulnerable to blaster fire, infantry can sometimes present a danger to the complex operations of the legs, or the vulnerable systems carried in the walkers underbelly.
As a result, the larger walkers are always escorted by the smaller AT-ST.
These light walkers target Rebel infantry and air power, blasting heavy weapon emplacements and blowing speeders out of the air.
Any Rebel caught out in the open is quickly run down and destroyed.
In addition, the AT-STs on Hoth carry special ground penetrating sensors to ensure the permafrost can bear the weight of the larger assault walkers.