The Battle of Gross-Jägersdorf was a major battle of the Seven Years' War that was fought in 1757 between an invading Russian army and the Prussian army of King Frederick the Great.
With Prussia surrounded by enemies, from France in the Rhineland to Austria in Silesia and Sweden in Pomerania, Empress Elizabeth of Russia entered the war on the Franco-Austrian side, and Field Marshal Stepan Apraksin was sent with 55,000 troops to cross the Niemen and capture Memel, which served as Russia's base for an invasion of East Prussia. The Russian invaders proceeded to brutally plunder the Prussian countryside, giving Frederick the impression that the undisciplined Russians would easily be defeated by his disciplined Prussian Army. He sent Field Marshal Hans von Lehwaldt with 28,000 troops to confront the Russians in East Prussia, where he ambushed the unprepared mob of Russian soldiers with a cavalry charge that inflicted heavy losses. The Russians degenerated into confusion, but Pyotr Rumyantsev rallied the Russian center. The Russian counterattack caused the Prussian assault to collapse, and the Cossack and Kalmyk cavalry lured Prussian soldiers into an artillery kill-zone. The Prussians managed to avoid encirclement by the Russians during their retreat, however, and proceeded to blockade the Swedish at Stralsund. A false report that Empress Elizabeth of Russia had died led to Apraksin retreating into Russia rather than overwhelming the rest of Prussia; Apraksin was relieved after Elizabeth recovered and found out that he had intended to support the succession of the pro-Prussian Peter III to the throne.