In the early morning, three attack helicopters take off from a secret base in Ukraine, flying low towards the eastern city of Bahkmut. As they approach their target, they suddenly rise, firing a hail of rockets, before taking a sharp turn and returning to their base, all at a dangerously low altitude. Since the beginning of the Russian invasion a little over a year ago, Ukrainian helicopter pilots have been flying dangerous combat missions every day at the controls of their old Mi-8 and Mi-24 aircraft.