As part of the Vermont National Guard, the school's Corps of Cadets was mobilized as a squadron of cavalry in the First Vermont Regiment to assist in General John J. Pershing's Mexican Expedition. This greatly disrupted the academic year and in 1916 the War Department designated Norwich as the first site for a Senior ROTC cavalry unit; also in 1916, the first African-American to attend the university, Harold "Doc" Martin (NU 1920), matriculated. Classes graduated early for both the First and Second World Wars and many Norwich-made officers saw service in all theaters of both conflicts. Professional education offered at Norwich also changed and adapted with the advance of technology. Military flight training began in 1939 and from 1946 to 1947, horse cavalry was completely phased out in favor of armored cavalry.