Originally from Monroe County, New York, Mansfield emigrated to Wisconsin prior to the Civil War.

[2] Following President Lincoln's call for 75,000 state militia troops in April 1861, at the onset of the Civil War, Mansfield was commissioned as captain of Company G, 2nd Wisconsin Infantry Regiment, known as the "Portage Guards.

[1][6][7] At Gettysburg, Mansfield had become major of the 2nd Wisconsin and was the 2nd highest ranking officer left in the regiment.

[9] Early in the fighting, 2nd Wisconsin soldier Private Patrick Maloney captured Archer himself, who surrendered his sword to Mansfield.

Archer's surrender to Mansfield marked the first capture of a Confederate general officer since Robert E. Lee had assumed command of the Army of Northern Virginia.

Invalid Corps, made up of men unfit for combat but able to assist in hospital work or other light duties.