By Nick Paton Walsh, Natalie Wright, Daria Makarina-Tarasova and Victoria Butenko, CNN. There's a whirring sound, a cloud of dust rises, there's a pause as the grainy image recalibrates, and then comes a devastating explosion. Underground, dozens of miles away, veterans of some of Ukraine's most brutal urban battles, in Avdiivka and Bakhmut, are now commanders of a new kind of killing: one they can't feel, smell, or see up close. A full-scale mi…