Described by some military commanders as the deadliest urban combat since World War II, the battle to drive ISIS out of Mosul as the terrorist group held civilians captive there was brutal and grueling. Shot over the course of the entire nine-month fight, this vivid documentary follows the experiences of four young soldiers in a team of Iraqi special forces tasked with leading the battle. Visceral footage of the fighting is interwoven with intimate and searching interviews with the young soldiers. Full of hope at the beginning of the campaign, the reality of fighting an elusive and vicious enemy in a city full of trapped civilians ultimately takes its toll: By the end of filming, one of the four soldiers is dead. And for the surviving soldiers, haunted by what they have seen and done, the war goes on.

Also this hour, FRONTLINE presents Inside Yemen –a rare, up-close look at the country that’s home to what the United Nations recently called the largest humanitarian crisis in the world. This short film reveals the consequences of two-plus years of airstrikes on the country by a Saudi-Arabia led and U.S.-backed coalition.