During World War I, the U.S. armed forces experienced a great influx of professional civilian musicians resulting, in part, from the mobilization of 27 African-American regiments to augment the U.S. Army's existing four black regiments. The regimental bands of these newly formed units were frequently led by black blues and jazz musicians experienced performing in the clubs of New York and Chicago. Among them was James Reese Europe, whose 369th Regiment band (the "Harlem Hellfighters Band") is credited with introducing jazz to Europe. Regimental bands during this time varied greatly in size and quality and "intensive recruiting by an ambitious colonel with a band fund and an able conductor might coax a significant number of voluntary enlistments and result in a flexible, professional-quality ensemble."