U.S. Representative Logan fought at Bull Run as an unattached volunteer in a Michigan regiment, and then returned to Washington where, before he resigned his congressional seat on April 2, 1862, he entered the Union Army as Colonel of the 31st Illinois Volunteer Infantry Regiment, which he organized. He was known by his soldiers as "Black Jack" because of his black eyes and hair and swarthy complexion, and was regarded as one of the most able officers to enter the army from civilian life. In a time when political generals usually performed poorly in battle, Logan was an exception.