In April 1941, the army was involved in the invasion of the Balkans, capturing Belgrade in a rapid offensive.

[1] It advanced from Białystok to Mogilev, Gomel, Chernigov, Bryansk successively and defended against Soviet counterattack near Kursk.

With Hans von Salmuth as the commander, it suffered a major defeat during the Voronezh-Kastornensk operation, the Soviet winter offensive that followed the battle of Stalingrad.

[1] General der Panzertruppe Dietrich von Saucken became commander of the army on 10 March 1945.

The army was renamed Army East Prussia (AOK Ostpreußen) on 7 April and was pivotal in the defence of East and West Prussia before end of World War II in Europe on 9 May 1945.