As seaman on board the USS Hendrick Hudson, St. Marks, Fla., 5 and 6 March 1865, Mack served with the Army in charge of Navy howitzers during the attack on St. Marks and, throughout this fierce engagement, made remarkable efforts in assisting transport of the gun. His coolness and determination in courageously standing by his gun while under the fire of the enemy were a credit to the service to which he belonged.