Why do i think that point is imp.....?  The number one reference for this wiki article.....is a book.....with the title.......of Union.......The Union's Secret War........

Union Spying[edit]

Allan Pinkerton (left) with Abraham Lincoln

The Union's intelligence gathering initiatives were decentralized. Allan Pinkerton worked for Maj. Gen. George B. McClellan and created the United States Secret Service.^[4] Lafayette C. Baker conducted intelligence and security work for Lieutenant General Winfield Scott, commander-in-chief of the U.S. Army. President Abraham Lincoln hired William Alvin Lloyd to spy in the South and report to Lincoln directly.^[4]

As a brigadier general in Missouri, Ulysses S. Grant was ordered by Maj. Gen. John C. Frémont to start an intelligence organization.^[4] Grant came to understand the power of intelligence and later put Brig. Gen. Grenville M. Dodge as the head of his intelligence operations that covered an area fromMississippi to Georgia with as many as one hundred secret agents.^[4]

Maj. Gen. Joseph Hooker, who became commander of the Army of the Potomac in January 1863, ordered his deputy provost marshal, Col. George H. Sharpe, to create a unit to gather intelligence. Sharpe set up what he called the Bureau of Military Information and was aided by John C. Babcock, who had worked for Allan Pinkerton and had made maps for George B. McClellan. Sharpe’s bureau produced reports based on information collected from agents, prisoners of war, refugees, Southern newspapers, documents retrieved from battlefield corpses, and other sources. When Grant began his siege of Petersburg in June 1864, Sharpe had become Grant’s intelligence chief.^[4]

The most useful military intelligence of the American Civil War was probably provided to Union officers by slaves and smugglers.^[11] Intelligence provided by slaves and blacks were called black dispatches.^[1