In 1880, Poenaru was promoted to lieutenant colonel,[1] and he became inspector of military engineers. In 1882, he was made commander of the first engineers’ regiment in the Romanian Army. In 1884, he was placed in charge of the officers’ school. Promoted to colonel in 1886 and to brigadier general in 1891,[1] he headed an army corps from 1896. He taught strategy both at the officers’ academy and at the Higher War School. In June 1894 he became War Minister, serving until October 1895. Together with Iacob Lahovary, Chief of the Romanian General Staff, he pursued institutional reform, modernizing the army's structure and cementing the special status of the general staff.[2]
From 1898 to 1901, Poenaru, from 1900 a division general, himself served as General Staff Chief, with Lahovary as War Minister. The two continued to collaborate, with Poenaru focused on updating mobilization plans and battle regulations. He also drew up plans for an eventual occupation of Austro-Hungarian ruled Transylvania, foreseeing a vigorous offensive from multiple directions. Finally, in the interests of monitoring the border with Austria-Hungary, he detached infantry battalions to the mountain passes of the Carpathians.[2]