During World War I, he was mobilized to the Imperial Russian Army and served in the Romanian Front where he became close friends with Antanas Merkys. This relationship proved crucial in Vitkauskas' career. He returned to Lithuania in 1918 and fought in the Lithuanian Wars of Independence. Thanks to Merkys, Vitkauskas became deputy commander of the Lithuanian Military Brigade and commandant of Klaipėda in the aftermath of the Klaipėda Revolt. Despite success in the field and evaluation as a capable officer, his military career was dampened by rumors and suspicions that he sympathized with the Bolsheviks and socialists. He resigned active duty in 1927 and worked as a lecturer at the Higher Officers' Courses in Kaunas. After the completion of training with the German Reichswehr in 1929, Vitkauskas became inspector of the infantry and helped Stasys Raštikis, commander of the army, to implement much needed reforms. He was particularly involved with practical training and military exercises. In October 1939, Vitkauskas led Lithuanian troops to Vilnius – the historical capital of the Grand Duchy of Lithuania which was fiercely contested between Lithuania and Poland since 1920. It was a prominent assignment that brought public recognition.