For extraordinary heroism on March 31 & 1 April 1865, while serving with Company A, 7th Wisconsin Infantry, in action at Gravelly Run, Virginia. On 31 March 1865, with a comrade, Sergeant O'Connor recaptured a Union officer from a detachment of nine Confederates, capturing three of the detachment and dispersing the remainder, and on 1 April 1865, he seized a stand of Confederate colors, killing a Confederate officer in a hand-to-hand contest over the colors and retaining the colors until surrounded by Confederates and compelled to relinquish them.