The first phase of the business lasts until the 24th of August, beginning with the 7th of that month, and may be very briefly dealt with.
Two Russian armies, numbering altogether perhaps 200,000 men, or at the most a quarter of a million, advanced, the one from the Niemen, the other from the Narew—that is, the one from the east, the other from the south, into East Prussia. The Germans had here reserve troops, in what numbers we do not know, but perhaps half the combined numbers of the Russian invasion, or perhaps a little more. The main shock was taken upon the eastern line of invasion at Gumbinnen; the Germans, defeated there, and threatened by the continued advance of the other army to the west of them, which forbade their retreat westward, fell back in considerable disorder upon Königsberg, lost masses of munitions and guns, and were shut up in that fortress. The defeat at Gumbinnen occupied four days—from the 16th to the 20th of August.
Meanwhile the Russian army which was advancing from the Narew had struck a single German army corps—the 20th—in the neighbourhood of Frankenau. The Russian superiority in numbers was very great; the German army corps was turned and divided. Half of it fled westward, abandoning many guns and munitions; the other half fled north-eastward towards Königsberg, and the force as a whole disappeared from the field. The Russians pushed their cavalry westward; Allenstein was taken, and by the 25th of August the most advanced patrols of the Russians had almost reached the Vistula.
The necessity for retaking East Prussia by the Germans was a purely political one. The vast crowd of refugees flying westward spread panic within the empire. The personal feeling of the Emperor and of the Prussian aristocracy in the matter of the defeated province was keen. Had that attempt to retake East Prussia failed, military history would point to it as a capital example of the error of neglecting purely strategical for political considerations. As a fact, it succeeded beyond all expectation, and its success is known as the German victory of Tannenberg.
The nature of this victory may be grasped from the accompanying sketch map.
From the town of Mlawa, just within Russian Poland, beyond the frontier, runs, coming up from Warsaw, a railway to Soldau, just upon the Prussian side of the frontier. At Soldau three railways converge—one from the east, one going west to Niedenberg and the junction of Ortelsberg, a third coming in from the north-east and Eylau.
Sketch 73.
From Eylau, through Osterode, the main international line runs through Allenstein, and so on eastward, while a branch from this goes through Passenheim to the junction at Ortelsberg.
Here, then, you have a quadrilateral of railways about fifty miles in length. Within that quadrilateral is extremely bad country—lakes, marshes, and swamps—and the only good roads within it are those marked in single lines upon my sketch—the road from Allenstein through Hohenstein to Niedenberg, and the road from Niedenberg to Passenheim. As one goes eastwards on that road from Niedenberg to Passenheim, in the triangle Niedenberg-Passenheim-Ortelsberg, the country gets worse and worse, and is a perfect labyrinth of marsh, wood, and swamp. The development of the action in such a ground was as follows:—