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, and 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. One Berserker was given the task to set off the explosive mines planted by the Uruk Hai.

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. Gimli himself accounted for three or more, hitting one in the chest and two in their nether regions.

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 amount 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.

Sappers
In the film and some of the game adaptations, there are also a few Berserkers that, rather than devastating the enemy front ranks with their powerful swords, handle and use Saruman's Fire of Orthanc bombs. In the Battle of Helm's Deep, they first placed many bombs in a small culvert in the Deeping Wall, the one weak spot in the impenetrable outer fortress. After the bombs are piled, one of the Sappers run forward with a lit torch, ready to light the bombs. Legolas attempts to shoot the Sapper with two arrows, but fails to bring the Uruk down before it lights the bombs, creating a huge breach in the Deeping Wall. The army of Isengard is then given a huge opening into the deeping wall, which they exploit immediately.

In the game adaptation, there are Uruk-hai that have Fire of Orthanc bombs strapped to their backs. These Uruk-hai attack by self-destructing themselves in a devastating explosion that damages all units around them, either friend or foe. This occurs whether the Uruk-hai are killed or they set off the detonation themselves. Though they can easily be taken down by arrows before they reach their target, if they do reach it, then the effect of the explosion is quite devastating indeed.