 Complete the following phrase:  We also know when the Civil War began in early 1861, he was commissioned a first lieutet in the Union Army though Joel Snyder, OSullivans biographer, could find no definitive proof of this claim in Army records. There is no record of him fighting. Alexander Gardner worked as a photographer on the staff of General George B. McClellan, commander of the Army of the Potomac, and was given the honorary rank of captain. Gardner described OSullivan as the Superintendent of my map and field work. Biographer James D. Horan writes that OSullivan was a civilian photographer attached to the Topographical Engineers. His job was to copy maps and plans, but he also took photographs on his own time. Although he later listed himself as a first lieutet, the rank was likely honorary, like Gardners. From November 1861 through April 1862, OSullivan, working for Gardner, followed Union forces to Fort Walker, 