Infantry units with sufficient manpower can detach a small unit of Skirmishers. Skirmishers can be deployed as a vanguard, or a screen, to engage and harass enemy units before they can engage the main body of friendly troops.
Detach skirmishers by selecting Infantry Orders (1) in the orders panel, then click Skirmishers (2). A small unit (3) fighting in loose formation is moved forward. By default, skirmishers are linked to the front of the detaching unit. You may give them independent orders, which will break the link automatically.
Skirmisher Detachments (4) do not suffer from order delays. They use their primary weapon (usually a musket or rifle-musket) to engage enemy units from a distance (5) and will automatically fall back if strong enemy units approach them. The Skirmishers suffer fewer casualties due to being spread out, and individual soldiers will fire more accurately, as they are not cramped shoulder to shoulder in a large formation.
While flexible, Skirmishers are not resilient to many losses (6) and will break sooner than whole units. They do not carry reserve ammunition and are not suited for melees (7).
If a Skirmisher detachment breaks, it will automatically reattach itself to its parent unit. You can also manually reattach skirmishers by pressing the same button (2) used to detach the Skirmishers.
If you give your HQ a stance, the commander under AI control may deploy Skirmishers on his own and use them to screen his formation.