In April 1898, at the outset of the Spanish–American War, Chanler responded to President William McKinley's call for volunteers by forming a New York regiment, with the encouragement of Theodore Roosevelt, who was hoping to lead it as lieutenant colonel. Known as the "Tammany Regiment," it was to be equipped at Chanler's expense. In early May, Governor Frank S. Black informed Chanler that the volunteer quota had already been reached by the 1st U. S. Volunteer Cavalry Regiment and that the army was unwilling to accept volunteer infantry, although Chanler speculated that it was in fact a politically motivated move.