On September 5, 1814, Flagg became a militia lieutenant in a small scouting detachment of teenage boys from the Plattsburgh Academy raised by captain Martin James Aikin (1791-1828).
General Alexander Macomb praised the Aiken's Volunteer Rifle Company for not falling back in disorder with the bulk of Mooers' militia during the fist encounters with the British invading force in the Battle of Plattsburgh [REF].