_Corps of Engineers._--1 brigadier-general, 4 colonels, 10 lieutenant-colonels, 20 majors, 30 captains, 30 first lieutenants, 10 second lieutenants. The battalion of engineers comprises a total of 805. _Ordnance Department._--1 brigadier-general, 2 colonels, 3 lieutenant-colonels, 6 majors, 20 captains, 20 first lieutenants, 12 second lieutenants, 15 storekeepers, and a battalion of 905 men. These figures all pertain to the _regular army_. A considerable number of the officers in the regiments have been appointed from civil life; but in the staff departments the officers are almost exclusively graduates from the Military Academy at West Point. The raising of the immense volunteer force necessitated a great increase in the staff departments, and large numbers of persons from civil life have been appointed into the volunteer staff in the Adjutant-General's, Judge-Advocate's, Quartermaster's, Commissary, Medical, and Pay Departments. The ordnance duties are performed by officers detailed from the line, and engineer duties by regiments assigned for that purpose. A large number of additional aides-de-camp were also authorized, forming that branch of duty into a department. Aides-de-camp are also detailed from the line. The highest rank yet created for volunteer staff officers is that of colonel in the aides-de-camp. The heads of staff departments at corps headquarters are lieutenant-colonels, including an assistant adjutant-general, assistant inspector-general, a chief quartermaster, and chief commissary. Many regular officers hold these volunteer staff appointments, gaining in this manner additional rank during the war--still retaining their positions in the regular service; in the same manner as many regular officers are field officers in volunteer regiments.