On December 23, in pursuance of an order of Maj. Gen. George H. Thomas, he was detailed to convey the captured flags taken by the 149th New York and other regiments to the War Department at Washington, and also received a leave of absence for twenty days, to take effect after the performance of such duty. For this service, no recognition was given at the time, but later Col. Barnum received the Medal of Honor. While absent in the performance of this duty, Barnum received further surgical treatment, and being disabled for field duty, was placed on recruiting service for the regiment, and again joined his command at Kennesaw Mountain, Georgia, about June 26, 1864, and a few days later was wounded by a fragment of shell in the right side at Peach Tree Creek, Georgia, July 20, 1864.