Within an hour of arriving in Afghanistan’s Sangin district last month, we heard jarring news: Marine units there had been attacked multiple times recently by grenades at close distances. How does an insurgent pull that off, you ask? The district’s “Fish Tank” area is a maze of high walls and tight alleys that allow Taliban fighters to creep uncomfortably close before launching an attack. Sure, they may not get away frequently. For a few fleeting moments, however, they still have the element of surprise. My last long-form story out of my recent embed in Afghanistan went online this afternoon, and…