He then joined the U.S. Army and was commissioned in May 1861 as a captain in the 13th Infantry, of which William T. Sherman, his brother-in-law, was colonel. He was appointed inspector-general on the staff of General Sherman, when in command of the western army. At the
Battle of Vicksburg he planted the flag of his battalion on the parapet of the Confederate fort, and received a severe wound. For this action he was brevetted major in 1863; for his action at Jackson, Collierville and
Missionary Ridge, in the
Atlanta campaign he was made lieutenant-colonel by brevet in 1864, and for gallant conduct in the march to the sea and thence through the Carolinas to Washington he was brevetted colonel in 1865. He was made brigadier-general of volunteers, March 8, 1865. ==Postbellum career==