Gand sign in Iraq (photo: FBI)                     
If  it’s not American gangs infiltrating the ranks of the U.S. military,  it’s the U.S. government infiltrating the ranks of Mexican cartels.
For the U.S. Army  and its auxiliary groups, keeping gangbangers out of the service has  become a serious problem. The FBI’s National Gang Intelligence Center  says the military is confronting a “significant criminal threat” from  street, prison and biker gangs whose members have enlisted in larger  numbers in recent years. According to the FBI, “members of at least 53  gangs have been identified on both domestic and international military  installations.” Some gangs call on their younger members, those without  criminal records, to infiltrate the military.
Going into the Army, Army Reserves or National Guard  (where most of the increase is happening) has allowed gang members to  acquire weapons and combat training, and then transfer these skills to  other members.
Meanwhile, federal law enforcement agencies are doing their own  infiltrating to combat violent Mexican drug cartels. The work has  involved establishing networks of informants into powerful criminal  organizations, and in the process, it has helped Mexican authorities  capture or kill about two dozen high-ranking and midlevel drug  traffickers.
-Noel Brinkerhoff
FBI Says Gangs Infiltrating the US Military (by Bryant Jordan, Military.com)
U.S. Agencies Infiltrating Drug Cartels Across Mexico (by Ginger Thompson, New York Times)
2011 National Gang Threat Assessment – Emerging Trends (National Gang Intelligence Center)
U.S. Drug Gangs Learn New Tactics by Fighting in Iraq and Afghanistan (by Noel Brinkerhoff, AllGov)