A military officer acting as secretary to a general is called this "de-camp"
The officer filling it was detailed from the officers of the line, ... of an adjutant
-general in the room of Colonel Pickering, who was called ... of Artillery, 
Continental Line), was secretary of the Western Territory, .... continued to perform 
the duties of aide-de-camp and of acting assistant adjutant-general to... [DOC] [TLE] The Military Staff - Civil War Trust [PAR] Civil War staff officers were vital to the operations of Civil War armies.