i want to be a spy i am looking forward to be clever and be a spy as well as i want to be a trainer
The answer above is from a prankster so a major edit is required.
General George B. McClellan hired the head of the Pinkerton Detective Agency to provide "intelligence" namely espionage, to help the Army of the Potomac assess the strengths and weaknesses of Confederate armies. Allan J. Pinkerton headed McClellan's military espionage bureau.
Another spy for the Union was acting independently from the Pinkertons, this was Pauline Cushman. Another spy of note for the Union was Elizabeth Van Lew.