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Letter from McClellan to Grant, late November 1864

"...one of the disadvantages that I discerned during the late war was the lack of precision in the systems of account for troops. You know of course, as do I, that a regiment consists of so many companies each of so many men - that is the establishment. But the establishment is so much more than the fighting strength that it quickly becomes hard to evaluate the true abilities of a regiment, or a brigade, or an army.
I commend to you the example of the British Armies which we latterly fought across the Northern States. In a British Army, a battalion is a formation of so many men - and that is the number of men who fight in the army. If they suffer casualties, their depots make up the numbers; their extra duty men are not accounted on the strength; they have no need to detach men for the duties of the army. So a battalion, unless recently harmed by a particular battle or cut off from replenishment, is a stable organization for which only the sick list (and that is a small list these days) impedes their effective functioning as they are supposed to be.
Conversely, in an Army of the United States, a Regiment is provided by the State with a set enlisted strength and then is left largely to fate. If it suffers from desertion - a problem which affects many regiments of Volunteers who sign up under an excess of zeal - then it is quickly diminished closer to 700 men of 1,000; if it has faced enemy fire, it may be down to 600; the men who are sick may diminish it to 500; then with the men who are detailed to bring the supply wagon for each company one may see a further reduction; even our own artillery makes draws upon our strength to make up the numbers for manning the gun, until what is supposed to be one thousand men can barely bring three hundred bayonets to the battle and so we create brigades to give the strength of an old regiment.
It seems to me that this system is inefficient; further, that it promotes imprecision. In the late war I recall more than once that the Commander-in-Chief asked of me why your own army was not able to defeat their foes, for it seemed to him that your strength was nearer forty-five thousand - for your number of regiments - than the twenty-two thousand you could place upon the battlefield. It further seems to me that this problem is one that bears considering for any future re-organization of the armed forces of the Republic - at the very least one could hope that a regiment should be replenished, to allow the new men to gain experience from their experienced peers..."

"...I would have the Present Under Arms be the strength measure by which we judge a regiment, or the Present for Duty equipped, not anything more and certainly not some nebulous Grand Aggregate of all the men who once signed a piece of paper..."