From Silver Sun Republic Codex

Cohorts are archetypes common to most class systems or grouping of like skills, for example, Heavy Infantry versus Archers versus Cavalry. In the Republic's Military Structure, Cohort Sergeants are considered part of the Staff system acting as special Staff Sergeants to assist in training, organizing, and developing weapons and tactics for use by the Republic.

Cohorts may conduct specialized and specific training, but do not generally exercise any significant command authority as a Cohort. Specialized units like Combat Engineers may employ Cohort Sergeants in command roles due to their highly specific and demanding requirements to best employ them.