The ground shakes as a U.S. Army M109A6 Paladin Howitzer fires a gas-propelled 155mm round as the unit calibrates the gun at Destiny Range in Mosul, Iraq, Apr. 23, 2010. The soldiers are assigned to the 3rd Infantry Division's 1st Battalion, 9th Field Artillery, 2nd Heavy Brigade Combat Team. (U.S. Army photo by Spc. Gregory Gieske)