On the afternoon of April 4, Army Lt. Col. Eric Schwartz was summoned to a command tent pitched in a dusty field 11 miles south of Baghdad. His brigade commander, Col. David Perkins, looked up from a map and told Schwartz he had a mission for him. "At first light tomorrow," Perkins said, "I want you to attack into Baghdad." Schwartz felt disoriented. He had just spent several hours in a tank, leading his armored battalion on an operation that had destroyed dozens of Iraqi tanks and armored vehicles 20 miles south. A hot shard of exploding tank had burned...