The Photographic History of The Civil War: in ten volumes, Thousands of Scenes Photographed 1861-65, with Text by many Special Authorities, Volume 5: Forts and Artillery.
Francis Trevelyan Miller, Ed.

McClellan was called to Washington and placed in command, and immediately, by his great energy, tact, and professional skill, restored confidence. On his assuming command of the Military Division of the Potomac, the field-artillery of the division consisted of no more than parts of nine batteries, or thirty pieces of various and, in some instances, unusual and unserviceable calibers. Calculations were made for an expansion of this force, based on an estimated strength of the new Army of the Potomac, about to be formed, of one hundred thousand infantry.

Considerations involving the peculiar character and extent of the force to be employed, the probable field and character of the operations, and the limits imposed by the as yet undeveloped resources of the nation, led to the adoption, by General McClellan, of certain recommendations that were made to him by General W. F. Barry, his chief of artillery. The most important of these were: to have, if possible, three guns for each thousand men; one-third of the guns to be rifled and either Parrott or Ordnance Department guns; batteries to be of not less than four nor more than six guns, and then followed a number of important recommendations concerning the tactical organization of the arm.

A variety of unexpected circumstances compelled some slight modifications in these propositions, but in the main they formed the basis of the organization of the artillery of the Army of the Potomac.

The supply of ordnance materiel before the Civil War was in large measure obtained from private arsenals and foundries. This sudden expansion in the artillery arm of the country overtaxed these sources of supply, and the Ordnance Department promptly met the requisitions of the chief of artillery of the Army of the Potomac by enlarging, as far as possible, their own arsenals and armories. The use of contract work was in some instances the cause of the introduction of faulty materiel; and the loss of field-guns on several