America’s Unknown Intelligence Czar

Just before the battle of Chancellorsville, the BMI produced an estimate that put Lee’ strength at 55,300—only 2 percent off the mark.

Within a few months Sharpe’s bureau was able to produce what would prove a deadly accurate tally of Lee’s army just before the Battle of Chancellorsville. By correctly identifying the Confederate order of battle down to individual regiments, and correlating hundreds of interrogations of prisoners, deserters, and refugees with other scraps of intelligence, the BMI produced on April 28,1863, an estimate that placed Lee’s strength at 55,300, a mere 2 percent less than today’s generally accepted figure of 56,500. A distinguished visitor who inspected Hooker’s headquarters at the time wrote that “we have a moral certainty of all that is necessary to know in regard to the enemy, every regiment and brigade, division etc., all the latest arrivals and departures, etc., all collated, compared from many sources and fully confirmed. The secret service of Gen. Hooker is far superior to anything that has ever been here before. . . . Nothing transpires in the enemy’s camp that he is not speedily informed of.” Besides indicating the strength and location of enemy units, Sharpe’s reports regularly supplied information on the whereabouts of artillery batteries, the state of repair of railroads, local topography, the locations of mines, the quantities of enemy supplies, troop morale, recent orders to the troops, and impending movements.

For the first time, the Army of the Potomac knew more of what was happening on Lee’s side of the Rappahannock than vice versa. And it was Sharpe’s work that directly made possible Hooker’s brilliant march on Lee’s rear at Chancellorsville a few days after his April 28 intelligence estimate, a coup undone only by Hooker’s subsequent sudden loss of nerve, which prevented the Union corps from following up their huge advantage. (Another intelligence coup at Chancellorsville was the discovery that the Confederates had broken the Union Army’s flag-signal code; Union signalmen then signaled a fake message that sent Jeb Stuart’s cavalry off in pursuit of a nonexistent Union cavalry raid.)

Constantly updating the enemy order of battle was Sharpe’s most potent weapon, for not only was it valuable intelligence in its own right but it served as a continual check on the reliability of information received from sources. As the historian William Feis notes in his book Grant’s Secret Service , every Confederate prisoner captured was asked by Sharpe’s interrogators to identify his regiment, brigade, division, and corps, when and where he had entered the front lines, and how and where he had been captured or why he had deserted. Sharpe later explained that “the state of our information” built up in this manner “has been such as to form a standard of credibility by which these men were gauged, while each was adding to the general sum.”

Sharpe’s interrogation reports are also notable for the swift and keen assessments of their sources’ credibility that almost always accompanied them: “From a reliable source"; “Honest but not intelligent"; “Informants are intelligent and not disposed to state more than they know to be true"; “All this is rumor but it comes from so many sources it is worth attention"; “Informant is very ignorant of the route he has taken or names of places he has been, so much so as to raise a doubt as to whether he has made the trip at all.”

Supplementing the intelligence derived from interrogations was a mass of reports from Sharpe’s own spies and scouts, from cavalry reconnaissance, and (less frequently but regularly) from intercepted enemy flagsignal messages, purloined letters, and “open sources,” such as Southern newspapers. Although Sharpe did not directly command cavalry or balloonists or Signal Corps observation posts, he was vigorous in obtaining their reports and fitting them into his growing matrix of knowledge about the enemy. On occasion, officers from his bureau were informally attached to cavalry units, to help steer their intelligence-gathering efforts where they were most needed.

All of this data flowed into Sharpe’s headquarters, which initially had a permanent staff of about 18 men that traveled with the Army of the Potomac’s headquarters and reported directly to Sharpe. Over time, the range of topics covered was immense, encompassing not just tactical military intelligence but also political, economic, and psychological intelligence about the Confederacy: the price of flour in Richmond, the schedule of train departures, the state of civilian morale.