Night's Watch Troop Tree
Night's Watch Recluit > Night's Watch Ranger
Night's Watch Ranger > Veteran Night's Watch Ranger or Mounted Night's Watch Ranger
Veteran Night's Watch Ranger > Elite Night's Watch Ranger or Night's Wach Longbowman

One way of getting this kind of troops is by capturing a castle and recruit rangers from it. Or capture a bunch of them and ask them to join you (this method lowers a lot of morale). The first one is recommended.

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