a series of train robberies during the 1850s, first bringing Pinkerton into contact with George B. McClellan, then Chief Engineer and Vice President of the Illinois Central Railroad, and Abraham Lincoln, a lawyer who sometimes represented the company. In 1859, he attended the secret meetings held by John Brown and Frederick Douglass in Chicago along with abolitionists John Jones and Henry O. Wagoner. At those meetings, Jones, Wagoner, and Pinkerton helped purchase clothes and supplies for Brown. Jones' wife, Mary, guessed that the supplies included the suit Brown was hanged in after the failure of John Brown's raid on Harpers Ferry in November 1859. American Civil War When the Civil War began, Pinkerton served as head of the Union Intelligence Service during the first two years, heading off an alleged assassination plot in Baltimore, Maryland while guarding Abraham Lincoln on his way to Washington, D.C., as well as providing estimates of Confederate troop numbers to General George B. McClellan when he commanded the Army of the Potomac. His agents often worked undercover as Confederate soldiers and sympathizers to gather military intelligence. Pinkerton himself served on several undercover missions as a Confederate soldier using the alias Major E.J. Allen. He worked across the Deep South in the summer of 1861, focusing on fortifications and Confederate plans. He was found out in Memphis and barely escaped with his life. This counterintelligence work done by Pinkerton and his agents is comparable to the work done by today's U.S. Army Counterintelligence Special Agents in which Pinkerton's agency is considered an early predecessor. He was succeeded as Intelligence Service chief by Lafayette Baker; the Intelligence Service was the predecessor of the U.S. Secret Service. His work led to the establishment of the Federal secret service. Military historians have been strongly critical of the intelligence Pinkerton provided for the Union Army, which for the most part was undigested raw data. In the view of T. Harry Williams, Pinkerton's work was "the poorest intelligence service any general ever had." Pinkerton's estimates of Rebel troop numbers, derived from his credulous interrogations of Confederate prisoners, deserters, refugees, escaped slaves ("contrabands"), and civilians unused to counting large bodies of men, badly exaggerated the size of those formations, sometimes almost doubling their actual strength. Pinkerton's numbers caused McClellan to consistently believe that he was drastically outnumbered by the Confederate forces he faced. McClellan's action in the face of what he believed