The Russians, after a remarkably quick advance through very difficult country, had now come within hail of the line of the Vistula. The line was protected by three first-class fortresses covered by at least four army corps in addition to the armies which had been driven back by the Russians. It was the critical moment of the campaign. With their heavy numerical superiority and strongly fortified position, the Germans would be sure to make a more determined resistance, and in greater force than any which the Russians had yet had to meet. In attacking the line Rennenkampf would be handicapped by a lack of heavy siege artillery, and by the numerical inferiority of his forces. On the other hand his troops comprised some of the finest fighting material in the world, they were flushed with victory and could be relied upon to make a tremendous effort to win the greatest triumph of all. If they could drive the Germans over the Vistula and bring up sufficiently large forces to invest Thorn, Graudenz and Danzig, the northern route to Berlin would be open to them as far as the Oder. The beginning of the end would indeed have arrived.
The Russians accordingly pushed forward. But they did not advance much further on the road to the Vistula. An immense German army, heavily supported by artillery, including numbers of the heavy siege guns which had already proved themselves to be the Kaiser’s most potent weapons, awaited the Russians in a strong position in the neighbourhood of Osterode, midway between Allenstein and Graudenz.
Von Hindenburg now proved himself to be a leader of remarkable skill and resource and he performed as brilliant a feat of generalship as the war has yet produced. Only a year before he had taken part in the manœuvres in East Prussia, and was acquainted with every inch of the ground. It was even stated that he had already solved the exact military problem with which he was now faced, and in the same locality. In addition he enjoyed the advantage of outnumbering the Russians by at least two to one.
These factors practically decided the battle. The district around Allenstein and Osterode is of the worst possible description for an invading force. It is a mass of lakes, swamps and forests, and an intimate knowledge of the locality is essential for the success of any military operations there. There are almost insuperable difficulties in the way of transport alone.
Utilising his advantages to the full, von Hindenburg lured the Russians towards Tannenberg to the south-east of Osterode. The Russians, realising that a successful offensive was their only chance, blundered forward. They pressed on until they found themselves in a position where their flanks rested on more or less solid ground, but their centre was backed by a vast swamp. Then von Hindenburg struck his blow. An immense force was hurled against the Russian right. A desperate encounter followed, but sheer weight of numbers gave victory to the Germans. The Russians were forced back on to the swamps. A similar attack on the Russian left was equally successful.
What followed was not a battle; it was one of the most hideous slaughters history has known. The Russians were unable to manœuvre on the swampy ground; the Germans, on the other hand, were in possession of the solid higher ground and free to move at will. From three sides they poured a murderous fire into the helpless Russians, forcing them deeper and deeper into the swamps. Guns sank in the mud, horses were unable to move, men stood up to their waists in the deadly slime. The carnage continued until nightfall, when Rennenkampf managed to escape with a remnant of his army, leaving Generals Samsonov, Martos and Pestitsch among the thousands of slain.
Thus von Hindenburg won the battle of Osterode and obtained ample revenge for his defeat at Gumbinnen.
The battle caused a complete reversal of the campaign. The route to Berlin via the north was not only barred, but the Russian advance was turned into a retreat. Hopelessly outnumbered, Rennenkampf was forced back on Allenstein. Every foot of the way was contested, but bit by bit he had to give up the results of his victorious move forward. Allenstein and Intersburg were in turn evacuated before the merciless pressure of the advancing Germans. The troops investing Königsberg were recalled. It was not until the frontiers were almost reached and strong reinforcements came up from Kovno and Grodno that the German advance was checked and finally held.
In spite of official attempts at secrecy, the news soon spread that the invasion of Germany upon which Russia’s Allies had placed such high hopes had ended in what appeared to be complete failure. Berlin was as far off as ever, and the Germans were at the very gates of Paris. Something had gone seriously wrong with the steam roller on which so much had depended!
The strategists were wrong in the blame they heaped on Rennenkampf’s head because of his failure. As a matter of fact, his chief fault was that he had played his part too well. He had never been expected to push forward so far as Osterode. His “advance” was intended simply to attract German attention and to prevent Germany from sending reinforcements to the Austrian army. In attaining this object he succeeded admirably. After the battle of Gumbinnen the Germans poured regiment after regiment of Landwehr and Landsturm troops into Eastern Prussia, which otherwise would have gone to the aid of the Austrians. Rennenkampf’s unexpected success took him too far forward. His advance was so rapid that it was difficult to bring up reinforcements. Osterode and its heavy losses was the penalty he paid for success.