the bulk of the forces for the operation consisted of the bulgarian 1st army with two corps composed of six infantry divisions and other smaller units (~100 000 troops) which advanced on the southern flank of the 3rd ukrainian front, with the 57th army positioned to its east (6th guards rifle corps, and 64th and 133rd rifle corps), and the other three armies of the front concentrated in the area between lake balaton and budapest. the south-western flank was occupied by the yugoslav partisans.