Corsairs - Pirates of the South

Pirates of the sea, slavers are the bane of Gondorian waters and when Sauron’s call goes out these Corsairs quickly answer for they want what is inside any great city – booty. Squat thick men, loud of voice and sleek black sailed ships, they attack the sea faring villages of Gondor not only to make their way up the river but to also demoralise the great nation. Though they are no match for the Dead army from Dimholt and they are quickly removed from the battle leaving Aragorn the many ships manned by the dead.
Bit of Trivia is that Peter Jackson (pictured) plays one of the Pirate Captains.

Dimholt - Those of the Dead

The men from Dimholt were a race of men that lived in the Mountains during the second age, when Elendil and Gil-galad called the free peoples of Middle Earth to fight Sauron these men did not come. Isildur then cursed them to the undead forever to haunt the passes of the border between Gondor and Rohan until their oath was fulfilled. They have neat armour and are commanded by a singular being that challenged those who come into their pass, “The way is shut, it was made by the dead and the dead keep it.” Thinking that Aragorn, Legolas and Gimli are more travelers that have ventured into their realm the dead challenge them but Aragorn wields Anduril, Flame of the West, the reforged sword of Narsil and calls them to fulfil their pledge, “What say you?”

Since no mortal can kill these undead creatures they are the perfect army and they attack the Corsair army giving Aragorn a perfect way to stop the back handed attack on Minas Tirith and the army then takes carry of the army that had put Minas Tirith under siege. Their oath fulfilled Aragorn lets them go and they finally return to the land of the dead, never to walk that of the living again.