Chickamauga (2nd day, 2 pm, Horseshoe Ridge - where small parts of many regiments stubbornly stuck fast in spite of the flood of retreating going on.)
Source: Chickamauga 1863: The River of Death
James R Arnold
Reed International Books Ltd 1997 p.77
Edit - I do not have a copy of the book indicated as the source for the bonus question, so I cannot verify the official answer. However, every player who answered this question said it was the 19th Ohio, not the 9th, so I am going to accept that answer.