After Romania entered World War I on the side of the Allies in August 1916, Tătăranu fought with the 2nd Battalion Vânători de munte, first as lieutenant, and then as captain.

Wounded in his leg during fighting at Izvoru in November 1916, he was evacuated to the Școala Centrală's hospital in Bucharest, where he was operated on by Doctor Marius Nasta.

[3]: 85  In May 1917, while on a train en route to an internment camp in Germany, he escaped again, together with two other fellow soldiers, and after a 210 km (130 mi) trek, mostly through the mountains, the three managed to cross the front line and rejoin the Romanian Army.

On 30 August 1941, Tătăranu signed in Tighina the Agreement Concerning Security, Administration and Economic Exploitation of the Territories between the Transnistria and Buh–Dnieper Region with General Major Arthur Hauffe.

On orders from General Friedrich Paulus, Tătăranu flew out of the Stalingrad pocket on 13 January 1943, to report to Marshal Ion Antonescu on the dire situation of the Romanian troops trapped there.