Army Group E
It was made up of volunteering Bulgarian workers and soldiers who did not agree with their government's decision to change their allegiance to the Allies. Only small numbers of pro-German Bulgarians were able to join outside Bulgaria, including some from the Fifth Army engaged in the occupation of Yugoslavia. The formation fought initially in occupied territories in Yugoslavia and Greece, in the corps under the command of General Friedrich-Wilhelm Müller. They fought to protected the retreat of the German Army Group E in the Vardar valley.