From eRepublik Official Wiki
Captains are appointed leaders of the Regiments and are a part of the command chain of the Military Unit. A Military Unit Commander can appoint Captains, as long as the Regiment has 20 or more full members.
Captains have the ability to set the Daily Orders for the regiments and remove members from their regiments who've been in the MU for longer than 2 days. Commanders are not able to remove/change captain orders until these battles end.
There are some special conditions you have to be aware about captains and daily orders:
- captains can set up to 5 daily orders a day
- "removed"/changed daily orders are still available until the specific battle ends
- captain orders concerning daily orders get a higher priority than commander orders
- commanders cannot change or remove daily orders set by captains until the current order ends