Berserkers

Berserkers were larger, even more fearsome versions of the Uruk-hai, standing about seven feet tall and weighing an estimated three hundred pounds. Before they were sent into battle, it is said, the bowl of their small, tight-fitting helmet was filled with the blood of their enemy, then pushed onto their heads. The intoxicating smell awakened a bloodlust that drove them to a battle-frenzy. Berserkers had no regard for personal safety, wore no armor except their helmets and were expected to fight to the death. Their sole object was to establish a bridgehead.

The Battle of Helm's Deep
For Helm's Deep they almost certainly would have been trained to climb onto the siege ladders as they were raised up against the Deeping Wall, then to buy enough time for their comrades who were swarming up the ladders and in behind the Berserkers. It proved very difficult to get close enough to wound the Berserkers, so although they only numbered about thirty they were able to inflict heavy losses on the defenders before they were finally all killed.

Weapons
Berserkers used only one weapon, a huge sword with a five-foot blade and a foot-long double spike at the end; it was a cumbersome sword, requiring an enormous ammount of strength to wield, but the eighteen-inch-long handgrip allowed the Berserker to apply leverage in the swing by placing his hands wide apart. Each side of the four-inch-wide blade was hammered to a sharp edge, and one blow from it could cut a man in a half. It was not an elegant or particularly efficient sword --- for example the spikes could get caught in the victim --- but the level of intimidation generated by such a nasty weapon was huge.