March 17, 1862 (Monday): The Pinkerton Estimate

Pinkerton on Horseback

HEADQUARTERS ARMY OF THE POTOMAC,
Washington, D. C., March 17, 1862.

Major General GEORGE B. MCCLELLAN,
Commanding Army of the Potomac:
   GENERAL: I have the honor to report the following information relative to the forces and defenses of the Army of the Potomac obtained to this date, which has been extracted from current statements made here by spies, contrabands, deserters, refugees, and prisoners of war, in the order of time as hereinafter stated, and which at the time of reception were made the subjects of special reports to you. I have also appended to this report of extracts from statements, and have made the same a part of this report, a varied summary of the forces and defenses of the rebel Army of the Potomac, showing by different combinations about the probable number of these forces and the locality and strength of their defenses:
By reference to the summary of this report it will be seen that 115,500 men is a medium estimate of the rebel Army of the Potomac, which are stated as being located as follows, viz: At Manassas, Centreville, Bull Run, Upper Occoquan, and vicinities, about 80,000 men; at Brooke's Station, Dumfries, Lower Occoquan, and vicinities, 18,000; at Leesburg and vicinity, 4,500; in the Shenandoah Valley, 13,000.
   Of the above-mentioned forces information has been received up to date, as shown by summary in this report, of the following specific organizations, viz: At Manassas, Centreville, Bull Run, Upper Occoquan, and vicinities, sixty-one regiments and one battalion infantry, eight regiments, one battalion, and seven independent companies cavalry, thirty-four companies artillery. At Brooke's Station, Dumfries, Lower Occoquan, and vicinities, eighteen regiments and one battalion infantry, one regiment and six independent companies cavalry, and fifteen companies artillery; in the Shenandoah Valley, twelve regiments infantry, two brigades militia, one regiment cavalry, and seven companies artillery; and at Leesburg four regiments infantry, one regiment militia, five independent companies cavalry, and one company of artillery.
   It is unnecessary for me to say that in the nature of the case, guarded as the rebels have ever been against the encroachment of spies, and vigilant as they have always been to prevent information of their designs, movements, or of their forces, going beyond their lines, it has been impossible, every by the use of every resource at our command, to ascertain with certainty the specific number and character of their forces. It may, therefore, safely be assumed that in so large an army as our information shows them to possess very much of its composition and very many of its forces have not been specifically ascertained, which, added to those already known, would largely increase their numbers and considerably swell its proportions.
   The summary of the general estimate shows the forces of the rebel Army of the Potomac to be 150,000, as claimed by its officers and as sanctioned by the public belief, over 80,000 of which were stationed up to the time of evacuation at Manassas, Centreville, and vicinity, the remainder being within easy supporting distance. This fact is strongly supported by the statement of several supposed reliable persons, to the effect that 80,000 daily rations were issued to the forces at Manassas, Centreville, and vicinity, and by the well-sustained fact that the portions of the army in the Shenandoah Valley and the Lower Potomac each had their separate commissary department and received their supplies from sources entirely independent of the department at Manassas.
   It will be seen by reference to several statements included in this report that the parties were engineers, conductors, & c., on the Manassas Gap Railroad, and that they testify under oath that their chance for information about the forces at Manassas and Centreville was the very best, and that the number stationed there up to about the time of evacuation was from 80,000 to 100,000. It is also shown by the statement of a refugee who resided near Fairfax Court-House that he learned from officers of the rebel army that the numbers of their forces at Manassas and Centreville were 75,000, and that 150,000 rations were drawn by the whole army.
   All of which is respectfully submitted by your obedient servant,* 



    E. J. ALLEN. [ALLEN PINKERTON.] 

* Much the same as report of March 8, p. 736. 


Official Records, Series I, Vol. 5, Part 1, Page 764.

Allen, from Scotland, was the first detective ever appointed in Chicago.  He also had a private practice and was summoned to Washington at the start of the war where he helped establish the Secret Service.  History widely condemns him for overestimating the rebel army McClellan confronted, contributing to his timidity.  But it is likely McClellan knew Allen’s estimates (overstated by at least 40,000 here) were inaccurate.  Partly to justify his caution, and later perhaps owing to him taking council of his fears, McCellan often cited Pinkerton’s figures.  Pinkerton arrived at them largely from interviews with slaves who had crossed over from Confederate lines.