Frederick occupied Silesia, except for three fortresses at Glogau, Brieg and Breslau, in just seven weeks, despite poor roads and bad weather. The fortress at Ohlau fell almost immediately, becoming an important supply magazine for Frederick's army. In late March 1741, Frederick set out on campaign again, but was forced to fall back by a sudden surprise attack by the Austrians. The first real battle Frederick faced in Silesia was the Battle of Mollwitz on 10 April 1741. Though Frederick had served under Prince Eugene of Savoy, this was the first time he had commanded an army. In the course of the battle, believing his forces had been defeated by the Austrians, Frederick galloped away to avoid capture, leaving Field Marshal Kurt Schwerin in command to lead the disciplined Prussian infantry to victory. Frederick would later admit to humiliation at his abdication of command and would state that Mollwitz was his school. Disappointed with the performance of his cavalry, whose training his father had neglected in favor of the infantry, Frederick spent much of his time in Silesia establishing a new doctrine for them.