On the 12th of September he was commissioned Major of the 12th. Regiment of Wisconsin Infantry, serving with it in Kansas, Missouri, and New Mexico. In October of 1862, he was assigned to duty on the staff of General McLean, as Inspector General of the first division, right wing of the Army of the Tennessee. He served in this capacity two months and was then assigned to duty on the staff of General James B. McPherson, as inspector General of the right wing of the Army of the Tennessee. In February, 1863, he was promoted to Lieutenant Colonel and became Assistant Inspector General of the Seventeenth Army corps. On the 20th of April, 1864, he was appointed Inspector General of the Department and Army of the Tennessee, serving in that capacity until the close of the war. He was chief of staff to General O. O. Howard, on the march to the sea and through the Carolinas to Beaufort, Goldboro, Raleigh and thence to Washington. At Atlanta he was promoted to a Colonelcy, dating from July 22d, 1864, for “gallantry on the field of battle,” and on the 21st of March, 1865, he was brevetted a brigadier general of volunteers, having attained this distinction while still under 24 years of age. After participating in the grand review of troops at Washington in May, 1865, General Strong was assigned with General Howard, to duty in connection with the conduct and management of the Freedman’s Bureau, and in September, 1866, was then mustered out of the service at his own request, having served in all over five years. Throughout his entire term of service he was recognized as a brave and capable officer, and his gallantry was attested on numerous occasions. It was he who raised the stars and stripes over the Courthouse at Vicksburg immediately after the capitulation of the confederate forces.