After a very successful career before the war, Hindenburg retired in 1911, only to be recalled to command the Eight Army in Prussia, with General Ludendorff as his Chief of Staff, on 22 August 1914. On arrival at Marienburg on 23 August, he approved Ludendorff and Col. Max Hoffmann's plan to counterattack and 'double envelope' Samsonov's Second Russian Army, which resulted in the German victory at Tannenberg (25-31 August 1914). Hindenburg and Ludendorff then directed the defeat of Rennenkampf's First Russian Army at the Masurian Lakes, directed the campaign against Poland, and succeeded at Lodz on 11-25 November.
Hindenburg was then appointed Commander-In-Chief of Austro-German forces on the Eastern Front, and promoted Field Marshal, operating first under Falkenhayn's direction and then on his own, effected the Gorlice-Tarnow breakthrough of May-June 1915 which resulted in the control of Poland. Despite these series of successes, the Russian Army continued in the field, and when divisions were transferred to the West to support the Verdun offensive, Hindenburg protested. With the failure at Verdun, and Roumania's attack against Hungary, Hindenburg successfully replaced Falkenhayn as Chief of the General Staff (29 August 1916), and he along with Ludendorff assumed de facto military control of the German war effort.
Hindenburg endorsed and oversaw the declaration of unrestricted submarine warfare, the ejection of Chancellor Bethmann-Holweg from office, along with the final offensive against Russia between July and December, 1917 and negotiated the 'Peace' of Brest-Litovsk on 3 March 1918. After the subsequent failures at the Somme, the Lys, the Aisne, Noyon-Montdidier and Champagne-Marne, despite the release of troops from the East, Hindenburg continued to preach 'defensive war.' His colleague Ludendorff was relieved of command on 24 October 1918, and replaced by General Wilhelm Groener, while Hindenburg remained Chief of the General Staff until January, 1919, when he submitted his retirement papers. He then subsequently returned to political activity on 26 April 1925.