Starting in October 1912, Olteanu was the inaugural commandant of the "Nicolae Filipescu" Military School at Dealu Monastery; he served in this position until August 1918.

[6] After Romania entered World War I in August 1916, Olteanu was put in command of the 2nd Călărași Regiment, and then served as Chief of Staff of the First Army Corps.

[8] In early December 1917, he was put in charge of the central command of the Romanian Volunteer Corps in Russia, based in Hârlău, Iași County.

For his role in securing the Maramureș region, King Ferdinand I of Romania awarded Olteanu the Order of the Crown, Commander rank, in a ceremony held at Baia Mare on 26 May.

[11] In late July the Romanian Army crossed the Tisza River and advanced towards Budapest, leading to the collapse of the Hungarian Soviet Republic.