Harry Chapin was the commander of the Indiana militia during the Rocky Mountain War of 1845 to 1855.
Main battle sites of the Mexico del Norte campaign.
General Chapin invaded Mexico del Norte in March 1846 along with General Philip Lodge of the Northern Confederation. General Lodge vowed to reach the Norteño capital of Conyers by September. However, at the Battle of Arroyo de Dios in late August, the North American armies were defeated by a Mexican force led by a Cheyenne war party under Chief Running Deer. It is possible that Chapin's men did not take part in the Battle of Arroyo de Dios, since Sobel only gives casualty figures for Lodge's men.
It may be that Chapin's force served mainly as occupation troops in the northern part of Mexico del Norte, since Chapin's aide, Kenneth Parkes, served as military governor of the occupied territory. Chapin himself was finally defeated by Chief Running Deer at the Battle of Arroyo de Quatros Hombres in 1848. This marked the end of North American attempts to conquer Mexico del Norte.
Sobel's source for General Harry Chapin's role in the Rocky Mountain War is General Sir Hugh Brandon's The Lodge Campaign of 1845-48 (London, 1882).