After the Estates General, the Empire re-organized its military forces into the "Imperial Security Force", a suitably pacifist name to suit the outlook of the new regime. This reorganization included an overhaul of the rank structure that eschews traditional ranks like "sergeant" and "lieutenant".
Here is a list of the ranks with a description, in brackets, of roughly what the rank translates to.
Senior Group Leader (Brigade Commander)
Group Leader (Regiment Commander)
Security Detachment Leader (Battalion Commander)
Security Unit Leader (Company Commander)
Unit Head Leader (Company 2IC)
Junior/Senior Unit Leader (Platoon Commander)
Senior Section Leader (Platoon 2IC)
Section Leader (Section Commander)
Of course, sort of like Starfleet, everyone in the Imperial Security Forces is an officer.