August 4th, 1915

- The next phase of the German offensive in central Poland opens today, undertaken by the southern wing of the German 8th Army and the northern wing of the German 12th Army (the latter the designation for General Gallwitz's force), concentrated east of the Narew River between Ostrolenka and the Bug River.  Their objective is the line Lomza-Wyszkow, and the main focus today is an advance along the Ostrolenka-Sniadowo railway, pushing back the Russian 12th Army.  To the south Warsaw, abandoned by the retreating Russians is captured.  The capital of Russian Poland, its fall is a major blow to the prestige of the Russian Empire, though given the course of the fighting on the Eastern Front since May its loss is hardly a surprise.  Further south along the Vistula at Ivangorod, the Russians evacuate the fortifications on the west bank of the river.

Gunners of the German 3rd Battery, 108th Field Artillery Regiment in their position on the Narew River, August 4th, 1915.

Meanwhile, realizing that the Russians are pulling back from the Vistula River, Mackensen orders the Austro-Hungarian 4th and German 11th Armies to drive north towards Kock and Parczew respectively, with their eastern flank covered by the Army of the Bug and the Austro-Hungarian 1st Army.  His ultimate objective is the railway connecting Warsaw and Brest-Litovsk, the capture of which would severely disrupt the Russian withdrawal.  By nightfall the Austro-Hungarian IX and XVII Corps are approaching Lubartow, and elements of the German 11th Army have penetrated the Russian line running through Rozkopaczow and Gorbatowka north of the Wieprz and Swinka Rivers.

- With the Russian withdrawal in central Poland, Conrad writes to Falkenhayn today to propose that the armies under Mackensen's command shift the direction of their advance from northwards to northeastwards; Conrad remains seduced by the vision of a massive encirclement of the Russian army, an ambition that was the basis of his disastrous operations in the first months of the war.  Falkenhayn remains unmoved, confident that such grand maneouvers are simply no longer practical.  Mackensen's advance to date has been accomplished by lavish supply and overwhelming concentration of force, not speed.  Not only would shifting the strategic objective to a breakthrough disrupt Mackensen's current plans, but its most likely outcome would be for the Russians to simply retreat further and the Germans to outrun their supply lines.