Smile, Taliban. The Marines are watching you. As mentioned in my new story outlining the current fight in Afghanistan’s volatile Sangin district, Marine forces in northern Helmand province are using tethered “spy blimps” to watch for insurgent activity. The most common is the Precision Ground Surveillance System, a 70-foot aerostat balloon that floats over many combat outposts up and down Route 611 from Sangin to Kajaki. Army Times colleague Lance Bacon wrote about their capabilities last month. First Battalion, 7th Marines, out of Twentynine Palms, Calif., also has one larger Persistent Threat Detection System, which carries hundreds of pounds of…