25 September
Russians regain control of the east bank of the Niemen River
Following the double defeats at Tannenburg and Masurian lakes, the Russian Armies in or adjacent to East Prussia were in bad shape, and the germans were preparing for further attacks. From 25-28 September, Rennenkampfs battered army counterattacked and managed to restore cohesion and stibilised the front, largely by regaining control along the Niemen
The previous actions had resulted in two defeats of the Russian army, and largely removed any threat to German forces stationed in East Prussia, although a Russian counter-attack from 25-28 September (the Battle of the Niemen) forced a German retreat back to the border and resulted in the Russian army retaking much of the ground lost in the First Masurian battle.
As a consequence of Tannenberg and the Masurian Lakes - although the former battle was a much clearer cut victory than the second - Hindenburg was hailed as a hero in Germany, subsequently succeeding Falkenhayn as Chief of the German Staff in late summer 1916.