breaking news. a massive battle under way tonight against isis, major offensive to end isis' reign over mosul. nick paton walsh is there on the front lines. he's witnessed the fighting and is "outfront." >> reporter: they've been waiting years to finally push through the lines and take on isis' brutality. when day came, it was still a dusty, slow grind. peshmerga into the desert to flank a main road to mosul. distinctive american vehicles are with western occupants in the convoy. air strikes often hitting the places they were headed to first. hopes isis might not fight for the tiny settlement surround mosul quickly dashed. this the first village they -- they move down the road toward mosul and they're encountering pretty heavy resistance. returning fire with what they have. which are often blunt and old.