Battle of Sienno

On 17 July 1915 the German troops of Colonel-General Remus von Woyrsch broke through the Russian positions at Sienno, between Iłża and Lipsko, on the west bank of the Vistula. The fight was decided within a single day: in the morning the Germans broke into the Russian lines, and by evening they had torn a gap in them about 10 kilometres wide. The breakthrough opened the way to the Vistula and the fortress of Ivangorod.

Woyrsch’s army group stood between the Pilica and the Vistula, on the left wing of the Central Powers’ forces conducting the summer offensive in the Kingdom of Poland. On the other side of the Vistula the Austro-Hungarian Fourth Army had since the beginning of July been engaged in heavy fighting at Kraśnik, and on 16 July Mackensen’s whole army group launched its great offensive on Lublin and Chełm. On 12 July the Austro-Hungarian high command ordered Woyrsch to attack at the same time, with a strong right wing, and to prevent the Russians from shifting troops to the other bank of the river. According to the Austrian official history he faced only two corps of the Russian Fourth Army of General Alexei Evert, the XVI and the Grenadier Corps, and the wing of the Second Army. Evert had earlier moved his remaining forces to the east bank, against the Austro-Hungarians.

Woyrsch concentrated three German divisions in front of Sienno and entrusted command of the attack to General Götz von König, commander of the Landwehr Corps. The corps consisted mainly of Silesian Landwehr regiments, that is, older reservists. The Austro-Hungarian group of General Hermann Kövess meanwhile had to stretch itself along an 85-kilometre front all the way to the Pilica. On 16 July the artillery shelled the Russian positions along the whole length of the front to conceal the point of attack. On the morning of 17 July the fire was concentrated on the sector at Sienno.

The reinforced Silesian 3rd Landwehr Division went in to the assault. It broke into the Russian position and by evening reached the stream of the Krępianka (PL), between Krępa and the eastern edge of Rzeczniów. According to the Austrian official history the gap was 10 kilometres wide and 6 deep. On its flanks, especially near Rzeczniów, the Russians were still putting up stubborn resistance, but their line on the west bank of the Vistula had already been broken. For this victory König was awarded the Pour le Mérite a few days later.

The next day the Russians were falling back along the whole sector. Behind their front the bridge over the Vistula at Solec was burning, and during the night of 18–19 July the Landwehr seized the crossings of the Iłżanka (PL) at Ciepielów and Kazanów. By then Woyrsch’s troops had taken about 2,000 prisoners and advanced 20 kilometres northwards. The breakthrough at Sienno, together with the defeat at Krasnystaw and the German offensive on the Narew, hastened the Russian command’s decision to abandon the line of the Vistula. Soon Woyrsch’s units stood before the positions covering the fortress of Ivangorod, for which the Germans and Austrians had already fought in the autumn of 1914.