Iraqi troops and their militia and volunteer allies were on the verge of declaring victory over Sunni militants holding the strategic town of Tikrit and were about to hoist the Iraqi flag over key government buildings, when, a survivor recalled Wednesday, “the doors of hell opened.” The Iraqi forces had apparently walked into a trap, and some soldiers — and many more of their untrained volunteer supporters — were either killed or badly wounded when the Islamic State in Iraq and Syria sprung it, according to accounts from two soldiers and volunteer leaders reached by telephone afterward. The debacle in Tikrit on Tuesday offered a vivid illustration of how badly the Iraqi military needs advisers. For weeks, the Americans had implored Iraqi leaders not to fight for the centers of cities, but to establish control of roads and highways, and thus set their own conditions for battle. […]