As well as e.g. the mace was the Warhammer a development of the early clubs and the associated principle of the weapon.
The function of a war or a beater was designed to deform the armor by the impact of his flat side so that the opponent was restricted in his movement or, depending on the impact point, got respiratory problems. A fatal effect would have the hammer usually achieved only in a hit on the head, for other parts of the body were usually fractures as a result of a hit.
Depending on the design of the hammer head, there was a striking pin next to the flat side. This was, as one imagines Dörner, tapering towards the end and could usually pierce armor effortlessly. Although no fatal injuries could be achieved, smaller injuries could limit or paralyze the opponent.
With the appearance of ranged weapons and the decline of heavy body armor also the war hammer lost its importance as a weapon towards the end of the Middle Ages.