Steffen entered the 32nd Wisconsin Volunteer Infantry Regiment in August, 1862; was with Ulysses S Grant in the Vicksburg Campaign in 1862–63; marched with William Tecumseh Sherman on the Meridian, Mississippi campaign in 1864: took part at the Siege of Atlanta and the Battle of Jonesborough; marched with Sherman to the sea and into South and North Carolina; took part in all the engagements with the command; marched through Washington, took part in the Grand Review of the Armies in May, 1865, and in June 1865 was mustered out.