When Major-General McClellan was appointed to the command of the Division of the Potomac (July 25, 1861), a few days after the first battle of Bull Run, the whole field artillery of his command consisted of no more than parts of nine batteries or thirty pieces of various and in some instances unusual and unserviceable calibers. Most of these batteries were also of mixed calibers, and they were insufficiently equipped in officers and men, and in horses, harness, and material generally.
My calculations were based upon the expected immediate expansion of the "Division of the Potomac" into the "Army of the Potomac," to consist of at least 100,000 infantry. Considerations of the peculiar character and extent of the force to be employed, of the probable field and character of operations, of the utmost efficiency of the arm, and of the limits imposed by the as yet undeveloped resources of the nation, led to the following general propositions offered by me to Major-General McClellan, and which received his full approval:
1st. That the proportion of artillery should be in the ratio of at least two and a half pieces to 1,000 men, to be expanded if possible to three pieces to 1,000 men.
2nd. That the proportion of rifled guns should be restricted to the system of the U. S. Ordnance Department, and of Parrott and the smooth bore (with the exception of a few howitzers for special service) to be exclusively the 12-pounder gun of the model of 1857, variously called the "gun howitzer," the "light 12-pounder," or the "Napoleon."
3rd. That each field battery should, if practicable, be composed of six guns, and none to be less than four guns, and in all cases the guns of each battery should be of uniform caliber.
4th. That the field batteries were to be assigned to divisions and not to brigades, and in the proportion of four to each division, of which one was to be a battery of regulars, the remainder of volunteers; the captain of the regular battery to be the commander of artillery of the division. In the event of several divisions constituting an army corps, at least one-half of the divisional artillery was to constitute the reserve artillery of the corps.
5th. That the artillery reserve of the whole army should consist of 100 guns, and should comprise, besides a sufficient number of light mounted batteries, all of the guns of position, and until the cavalry was massed all the horse artillery.
6h. That the amount of ammunition to accompany the field batteries was not to be less than 400 rounds per gun.
7th. A siege train of fifty pieces. This was subsequently expanded (for special service at the siege of Yorktown) to very nearly 100 pieces, and comprised the unusual calibers and enormously heavy weight of metal of two 200-pounders, five 100-pounders, and ten 13-inch sea-coast mortars.
8th. That instruction in the theory and practice of gunnery, as well as in the tactics of the arm, was to be given to the officers and non-commissioned officers of the volunteer batteries by the study of suitable test-books and by actual recitations in each division, under the direction of the regular officer commanding the divisional artillery.
9th. That personal inspections, as frequent as the nature of circumstances would permit, should be made by me, to be assured of the strict observance of the established organization and drill and of the special regulations and orders issued from time to time under the authority of the commanding general, and to note the progressive improvement of the officers and enlisted men of the volunteer batteries, and the actual fitness for field service of the whole, both regular and volunteer.
[10th.] A variety of unexpected circumstances conspired to compel in some degree trifling modifications of these general propositions, but in the main they scrupulously formed the basis of the organization of the artillery of the Army of the Potomac. This sudden and extensive expansion of the artillery arm of the nation taxed far beyond their capacities the various arsenals and private foundries which had hitherto exclusively supplied to the United States the requisite ordnance material. The Ordnance Department promptly met my requisitions by enlarging as far as possible the operations of the arsenals of supply and construction and by the extensive employment of private contractors. The use of contract work, while it gave increased facility in meeting