September 17th, 1915

- General Alexeiev of West Front concludes today that even with the formation of 2nd Army east of the Sventsiany gap, Vilna can no longer be held in the face of the threat of the German offensive cutting the line of retreat of the city's defenders.  Orders are thus issued for 10th Army to withdraw from the city eastwards.

- At dawn elements of the Russian XXXIX Corps, advancing from the confluence of the Putilowka and Stubiel Rivers, crash into the Austro-Hungarian 62nd Division.  Already battered after severals days of combat, and with its southern flank uncovered by the retreat of 24th Division, 62nd Division quickly breaks, and its shattered remnants can only retreat westward as fast as possible.  Further north, Russian cavalry break through the Austro-Hungarian cavalry corps under General Berndt at Zurawicze and Karpilowka while the Russian IV Cavalry Corps pushes back the Austro-Hungarian 1st Cavalry Division.  By late morning the retreat of the Austro-Hungarian cavalry has uncovered the northern flank of 4th Army, and there are no more reserves immediately available to restore the situation.  The commander of 4th Army concludes that there is no alternative to a large-scale retreat to put space between his forces and the Russians and give time for his infantry to rest and recover - 4th Army has suffered 50 000 casualties since the beginning of the offensive towards Rovno a month ago.  Conrad reluctantly agrees with this assessment, and orders are issued for 4th Army to retreat all the way to the Sytr River, which also compels the northern wing of 1st Army to fall back on the Ikwa River.  After dark the exhausted Austro-Hungarian forces disengage from the Russians and begin their retreat, and the retreat begins after dark.

The collapse of 4th Army also compels Conrad to once again ask Falkenhayn for aid.  To the north of 4th Army, the German Army of the Bug has continued its successful advance, capturing Pinsk yesterday.  Conrad proposes that a significant portion of the Army of the Bug be diverted to the southeast to fall upon the northern flank of the now-advancing Russian 8th Army.  Falkenhayn agrees, but insists that the operation be placed under a German commander.  In no place to resist the suggestion, Conrad concurs, and General Linsingen, commander of the Army of the Bug, is made head of an army group that is to consist of the German XXIV Reserve Corps and the German 5th Cavalry Division from the Army of the Bug as well as the Austro-Hungarian 4th Army and the two Austro-Hungarian cavalry corps operating between the two armies.

- In Bulgaria opposition leaders secure an audience with King Ferdinand where they demand the recall of the Bulgarian parliament to debate entry into the war and warn the monarch that the Bulgarian people will not tolerate going to war with Russia.  Ferdinand, however, is not to be dissuaded from his chosen course of action, and merely promises to relay their concerns to Prime Minister Vasil Radoslavov.