Russian army defeated at Masurian Lakes.
The Battle of Masurian Lakes was fought in September 1914. Masurian Lakes was the second defeat for the Russian Army in World War One at the hands of the German army – the previous month had seen the destruction of the Russian Second Army at the Battle of Tannenburg.
Just as Ludendorff and Hindenburg had seen off Samsonov at Tannenburg, they wanted the second part of what had been intended as a Russian pincer movement in East Prussia defeated – Rennenkampf’s Russian First Army. With Samsonov’s Second Army defeated, Rennenkampf was in a much weaker position in East Prussia. If Rennenkampf’s force was taken out, then Germany’s eastern border was much more secure from attack and the potential existed to transfer men to the Western Front.