CASUALTY RECORD // September 7, 1914
First Battle of the Masurian Lakes
Estimated casualties — killed, wounded, captured, and missing — by side, with confidence labels per surviving record.
Casualties by side
2 sides catalogued · combined 101,914–126,914 estimated
Germany
1,914
Medium-confidence figure
Russian Empire
100,000–125,000
Medium-confidence figure
Battle context
The First Battle of the Masurian Lakes followed within days of Tannenberg, extending Germany's operational success on the Eastern Front by targeting the remaining Russian force in East Prussia. Hindenburg and Ludendorff turned the 8th Army against the spread-out Russian 1st Army under Rennenkampf, using the East Prussian railway network to reposition forces with a speed the Russians could not match. The result was the ejection of the 1st Army from German territory across its entire front, completing the removal of Russian forces from East Prussia that Tannenberg had begun against the 2nd Army. German casualties were a fraction of the Russian total, which reached between 100,000 and 125,000 against roughly 1,900 German losses, underscoring the scale of the operational asymmetry. The offensive stalled when the Russian 10th Army appeared on the German right flank, capping the advance and preventing a deeper encirclement, but the strategic effect was clear: the Russian invasion of East Prussia had been reversed in under three weeks.
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