The original Steamfantry dates back about half a century ago. It was during these clockwork ages that the first serialization of war machines began taking advantage of limbic technologies. These barely yielding heavy iron armors got equipped with piston muscles. A simple, but sturdy design, which still provides unmatched defensive abilities and is nearly indestructible.
The defensive Steamfantry went obsolete when the empire started to focus more on the development of mobile units to quickly decide battles for themselves, so the old technology was not up-to-date with the new strategies. After the enemy had adapted to these highly offensive tactics however, the need for a strong defensive units arose again, and the quick solution was to retrofit the old suits of armor.
The newly adjusted Steamfantry proved to be stunningly effective. In the battlefields of the cold North the engine and pistons counteracted glaciation and kept the pilot nice and cozy in unbearable heat. Said engines were smaller, more powerful, and fuelled by diesel; giving the units speed and mobility, completely overshadowing its predecessor.
The most efficient way to disable the adjusted Steamfantry is to push it over. Against such acts it can brace its massive bladed shield into the ground to gain additional stability. That is, if anyone manages to get through the fire of the calamitous minigun mounted to it's arm.
And even if the unit is downed, the surviving chances of the soldier are fairly large, the pilot must only await the support of allied forces.