You will notice that the level HELM'S DEEP: THE BREACHED WALL is very difficult to pass. In the last part of the level the Uruk-Hai bring an explosive cart. The energy of the door that you have to protect will be almost gone. The cart will shoot many explosives. The trick is to go past the cart guards and kill the orc that is operating the explosive cart. After killing him the cart won't shoot any explosives. Kill the cart guards and destroy the cart. You will complete the level and save the door from being destroyed.