"It was at this time that a large band [of orcs] came so far west as to enter the Shire, and were driven off by Bandobras Took."
—Appendix A, The Lord of the Rings
Mount Gram was long inhabited by a group of Orcs led by their chief (until the year 2747 of the Third Age), Golfimbul. They terrorized some of the inhabitants of eastern Eriador which included the Shire. In TA 2747, the growing troops of goblins from Mount Gram attacked the Shire and so caused the Battle of Greenfields. Those orcs fell in battle against Bandobras Took, and their leader Golfimbul was killed by him.
This unit has no abilities. This means that apart from the stances, which are present in every unit, it cannot affect the game play apart from his direct attack. This includes both passive and active abilities
This unit has no upgrades. This means that this unit can not gain any sort of permanent boost from upgrades found in either its palantir or from other units/heroes. If this is not the case, fill in the section following the policy.
The Orc Slayers are just regular swordsmen without any specific abilities. However, they are still stronger than the thrall master melee units. As a summoned unit, you don't have to worry about keeping them alive as much. Therefore, they have many uses and can be thrown into battle without caring about their eventual death. They can be summoned when you are outnumbered to even the odds. They can be summoned behind enemy lines to prevent the army or a hero from escaping the battle. There is also the mental effect on your opponent as they are suddenly surrounded and outnumbered. Since they have a timer, you shouldn't waste them after a skirmish is won. Instead, send them to chase the fleeing army or to attack any enemy buildings that are undefended.
The Orc Slayers can be combined with extra things to make them more effective. These include Horn of Angmar to boost their strength, Dark Obelisk to weaken the enemy, or Fell Wind and Helegwen's Freezing abilities to leave the enemy open to attack.