Battle on the first day of Russia's invasion of East Prussia (First World War). The Russian First Army under General Pavel K. Rennenkampf, invading from the east, was spread out over too wide a front. It ran into a single German army corp under General Hermann von Francois, and was badly mauled. Rennenkampf temporarily withdrew to the border, having lost 3,000 men, in what would compared to later battles appear to be a minor skirmish. Francois withdrew to Gumbinnen.