Complex sentence: War hammers, especially when mounted on a pole, by impact alone, could damage without penetrating the armour, in particular they transmitted an impact through even the thickest helmet and skull to damage the brain against its own skull.
Split into simpler sentences: War hammers, especially when mounted on a pole, by impact alone, could damage without penetrating the armour. In particular, they transmitted an impact through even the thickest helmet and skull to damage the brain against its own skull.