Ukraine has been through several stages of national security orientation: non-alignment, aspiration to join NATO, non-alignment and orientation on Russia and, since 2014, defence from Russian aggression and aspiration to join NATO in the future. The inconsistencies in national strategies have led to confusing military doctrines and an ineffective military posture. In 2014, the response of Ukraine’s armed forces during the Russian annexation of Crimea and in the early phase of the operations against pro-Russian separatists proved rather poor, and exposed serious military weaknesses, except the will to defend the country. Over the next two years, Ukraine took a number of measures of mobilization and rearmament, and thereby managed to rebuild a substantial force capable of stopping the Russian invasion and separatism in Ukraine’s south-east. Further on, capitalizing on lessons learned and Western support, Ukraine intensified its defence transformation to make its armed forces capable of deterring full-scale aggression from Russia.