TALL AFAR, Iraq — The last time the 3rd Armored Cavalry Regiment served in Iraq, in 2003-04, it was distinguished by a series of abuse cases growing out of its tour of duty in Anbar province. But its second tour in Iraq has been very different, according to specialists in the difficult art of conducting a counterinsurgency campaign — fighting a guerrilla war but also trying to win over the population and elements of the enemy. In the past nine months, the regiment has focused on breaking the insurgents' hold on Tall Afar, a town of 290,000. U.S. military experts...