On April 17, 1861, John enlisted as a private in the Rhode Island 1st Infantry and was “slightly” wounded (according to his obituary, dated 10/15/1910) at the Battle of Bull Run on July 21, 1861. After three months of service he enlisted in the First Rhode Island Cavalry. He was quickly promoted to sergeant and “later for bravery in action was promoted to Captain of his troops” (from the above mentioned obituary)
He was eventually promoted to Lt. Colonel and commanded the First RI Cavalry.
His obituary lists some of the over 50 battles he fought in, including Fredericksburg, Gettysburg, Cedar Creek, and Petersburg.