Units are the primary unit of organization between you and your soldiers, allowing you to set orders and manage hundreds of individuals soldiers at once. Each unit under your command will have it's own supply source, battle strategy, tactics, name, and deployment settings, allowing you as their leader to maximize their use on the field. At this time, many of these settings, with exception for unit name and supply source, are not implemented.
Generally speaking, units are best when made up of soldiers all using relatively the same equipment. Archers with archers, cavalry with cavalry. In battle a unit will only move as slow as it's slowest soldier, and while it can be said that a disorganized mess is hard to fight against, it's also hard to deploy effectively.
For more detailed guidance on how exactly units work in the field, we recommend you read the Battles page.
You can station units at your estates or you can have them follow you around as a mobile army. You cannot send units out on their own, they always need to be led by a player character.
Militia (units stationed at estates) will always automatically defend a settlement when it is being attacked. Mobile forces only defend settlements they are at automatically if they have the "defend settlement" action set. Otherwise they need to explicitly join the battle.
As the world we simulate does not have professional standing armies, stationed militia continue to work their old jobs for half of the day and thus contributes to the local economy and resource production. They cannot, however, be used for construction work. Recruits in training need all their time for training and do not contribute to the local economy.
Gone are the days of First Ones telling the mortals to steal from the locals in order to feed themselves--apparently, even at the behest of a First One they weren't too happy about it--now this is handled entirely under "supply". Supply is either drawn from a settlement under your command, the settlement of the Unit's origin, or the settlement of someone who has agreed to supply you. Presently, this is strictly for food, but once a proper method to delay arrival of goods is added, this will also allow field resupply of armor, weapons, and other gear.
Past Supplies, there are two main things you'll concern yourself with in regards to Units: Strategy and Tactics.
Strategy is your unit's course of action when in battle. Specifically, where it will try to orient itself in relation to opposing forces, and from which direction it will attack them. Each strategy is detailed below:
Tactics, on the other hand, is how they will engage the enemy. Will they use ranged weapons? Melee? Or whatever is appropriate? "Use Best" is normally the best choice but we're sure there are strategies out there that say otherwise.
Simply put, these control where your forces deploy in relation to their allies and enemies and whether or not they'll leave fortifications to attack an enemy. They let you fine tune your forces time to encounter as well as make effective use of walls (which give a handy bonus to defenders). This defaults to Line 4, the middle, if not set.
Units will usually have a home base, and the lord of their home base is the person who has final say on whether a unit remains deployed or not. The lord of a unit's base will be able to train new soldiers for a distant unit or outright recall them. Both of these actions will involve travel times that will prevent a unit from being assigned otherwise. If you find yourself no longer in need of a unit in the field, you can also opt to return them yourself.
Units can also be rebased to another settlement. Typically this requires the lord to command the unit and be in another settlement, but if the unit is currently without a base to work from, this can be done by the character commanding the unit.
Taking a first one captive will also take their units captive. However, units and their leader are handled separately for captivity purposes, and captive soldiers cannot be reinforced or recalled, and the captor will gain some limited setting management. It is entirely possible to release the units to go back to their base while keeping the first one, or releasing the first ones while holding their soldiers captive.