IIRC:
Black gangs members sign up for military service so they can learn tactics, materiel, handling, etc.
e.g.,
http://www.businessinsider.com/fbi-gang-assessment-us-military-2011-10
Gangs encourage members, associates, and relatives to obtain law enforcement, judiciary, or legal employment in order to gather information on rival gangs and law enforcement operations. Gang infiltration of the military continues to pose a significant criminal threat, as members of at least 53 gangs have been identified on both domestic and international military installations. Gang members who learn advanced weaponry and combat techniques in the military are at risk of employing these skills on the street when they return to their communities.
Gang members are acquiring high-powered, military-style weapons and equipment which poses a significant threat because of the potential to engage in lethal encounters with law enforcement officers and civilians. Typically firearms are acquired through illegal purchases; straw purchases via surrogates or middle-men, and thefts from individuals, vehicles, residences and commercial establishments. Gang members also target military and law enforcement officials, facilities, and vehicles to obtain weapons, ammunition, body armor, police gear, badges, uniforms, and official identification.
https://www.fbi.gov/stats-services/publications/2011-national-gang-threat-assessment
Yup. They were doing it in the '80s when I went in. Not so much in the Air Force, but we heard stories here and there about them. Mostly Army, but some were Marine Corps.