In late June, just two weeks into his tour here, Pvt. Jeremy Kretz from Dubuque, Iowa, was driving in a convoy near the border with Pakistan when a remote-controlled explosion hit his Humvee, causing him to black out and blasting him and his companions with rocks and dust. The American soldiers got away with concussions, ruptured eardrums and gravel-peppered skin. “Head’s pretty full of gravel anyway,” joked his commander, Lt. James Avrams, who is in charge of the protection force at Gardez, raising a laugh among his men, all from the 34th Infantry Division, Iowa National Guard. But for the American military, and foreign and Afghan officials, remote-controlled explosions have become the biggest threat in Afghanistan. Although they are not being used on nearly the scale found in Iraq, they are becoming more common and increasingly sophisticated, military and other officials said in interviews. About OODA Analyst