Mack changes his mind by September 12, when the Austrians occupy Munich, and discards his earlier plan, to the dismay of Archduke Ferdinand.

He decides to concentrate his army farther west on the Iller River so he can counterattack any French invasion coming through the Black Forest.

As part of his new strategy, Feldmarschall-Leutnant Franjo Jelačić (also Franz Jellacic) is ordered to move from Feldmarschall-Leutnant Archduke John's Army of the Tyrol to Lake Constance.

Mack expects to have fifty thousand to fifty-five thousand troops in position near Ulm by the end of September.

Jellačić will hold the left flank with eleven thousand soldiers while Feldmarschall-Leutnant Michael von Kienmayer twelve thousand-man corps watches the Bavarians from Ingolstadt.

However, the change of plans throws the Austrian army's supply system into disarray.