With the annexation in 1938 of Austria by Nazi Germany, what was once the 4th Austrian Division was incorporated into the Wehrmacht (German Army) and re-designated the 45th Infantry Division. In the 1939 Polish Campaign, the division was on the right wing of von Rundstedt's Heeresgruppe Sud (Army Group South).
On 22 June 1941, the 45th Infantry Division began Operation Barbarossa by starting the 9-day long siege of the Brest Fortress. In March 1942 the Red Army defeated the division at Livny, Russia and captured the archive of the division. That was the first time the Red Army learned about the defense of Brest Fortress
^Christian Ganzer: German and Soviet Losses as an Indicator of the Length and Intensity of the Battle for the Brest Fortress (1941). In: The Journal of Slavic Military Studies, Volume 27, Issue 3, p. 449-466.
^Бешанов В.В. ”Бресткая крепость” Минск, 2004 (in Russian) page 130