ATO (Anti-terrorist Operation in the East of Ukraine) – multiple actions against illegal military units that occupied a part of the Donetsk and Luhansk oblasts in the east of Ukraine. The so-called ‘Russian Spring’ in Donbass, inspired and supported by Russia, started in spring 2014 after the annexation of Crimea. Ukrainian authorities, considering the hybrid nature of the aggression and trying to prevent the repetition of the scenario from the early 90s’, when the Russian army was operating in the territories of other countries as ‘peacekeepers’, decided not to impose the martial law, but to declare an anti-terrorist operation. ATO began on April 13, 2013, when Sloviansk, a town in Donetsk oblast, was occupied by unidentified, armed people coming from Russia. In the photos unidentified, armed people, who occupied the town of Sloviansk in April 2014. In the photos soldiers of the special unit of the Ukrainian Security Service attacking positions of militants in the suburbs of Sloviansk. Probably it was only a reconnaissance. The name ATO has been criticized because of the nature of the combat operations carried out, which does not resemble classic anti-terrorist operations, but war battles with the use of large military units and heavy weapons: artillery, tanks, etc.