On 12 May 1759, Platen was promoted to "generalleutnant", and was given command of the cavalry in the army of Prince Henry, the King's brother, operating in Saxony. The prince sent Platen on a successful marauding expedition with Frederick William von Kleist to the Bamberg area; afterward, Platen joined the King's army for the Prussian loss at Kunersdorf. In May 1760, he was sent, with General Friedrich Wilhelm Quirin von Forcade de Biaix, to the Pomeranian Neumark, with instructions to halt the advance of General Gottlieb Heinrich Totleben and his Russian army into Prussia. Subsequently, Platen was ordered to Landsberg to block the approach of the Russians and Austrians into Silesia and, most importantly, to defend the city of Breslau. Despite his efforts, in October 1760, the Russians under command of Totleben and Ivan Chernyshyov, and the Austrian army commanded by Franz Moritz von Lacy, occupied Berlin.