A juggernaut is a berserker who has chosen to wear armour, while this slows them a little, the damage they can cause from crashing into the enemy lines is improved greatly. They become such an unstoppable force that don't try to come to a stop themselves, but gradually turn in large arcs, all the while swinging their large weapon around and felling enemies on mass. Clad in a full suit of heavy armour deflects most damage, while their resilience allows them to ignore the rest.
Juggernauts excel in large battles they are left to their own plan, causing such a distraction to the enemy commander and have the space to move where their momentum carries them. Similarly they relish tight spaces like tunnels, as there is no where to run. In small battles juggernauts are directed to the biggest threat as a method of distraction and the enemies will not be able to block them.