During times of peace Constables serve as hands and eyes of the Sheriffs. They are rank-and-file law keepers whose task is to maintain order in colonies and resolve matters that are too low-level (or too numerous) for Sheriffs to handle.
When the need arises Constables lead teams of Militia Gunners serving both as squad officers and as examples for other colonists. Though they have almost the same gear as regular Militia, additional combat experience allows Constables to show much better results on the battlefield. Besides, their presence keeps Gunners from uncoordinated actions and even helps to maintain order and keep Human units from routing, should the situation change for the worse.
On several occasions Constables had to take command of Militia forces when their Sheriffs were killed or otherwised removed from the fray. Though they did not possess either the sophisticated (by FALCON standards) communication equipment or authority as their superiors, those brave men and women did their duty and saved the day.