 In 1864, he served with distinction in the Chattanooga and Atlanta campaigns and in the March to the Sea under William T. Sherman.He was severely wounded three separate times but survived the war.On January 13, 1866, President Andrew Johnson nominated McCook for appointment to the grade of brevet brigadier general of volunteers, to rank from March 13, 1865, and the United States Senate confirmed the appointment on March 12, 1866.