Kalran: Tales of the four nations/Volunteer center

Volunteers, citizens of Ouroboros who chose to fight and defend their government, are uber-infantry, which have the combined features of tanks and infantry. Volunteers are uncrushable by normal vehicles, and in fact some of the heavier ones can crush infantry. They are resistant to anti-infantry weapons but takes a bit more damage to anti-tank weapons. They can garrison structures as well and are the only units, barring the commanders epic, that can gain veterancy.

But Volunteers requires mandate to purchase and they only come as a single unit, meaning its going to be harder to create large squads, and are universally fragile, or close to, meaning they must rely on the more numerous penitent infantry, vehicles, and naval craft, which can't gain veterancy, to protect them.