"The Czar trusted me.  How can I face him after such a disaster?" - General Samsonov, 29th August, 1914

Gospodin General-Major, our reconnaisance battalion has come across wayward troops from XV and XIII Corps of the 2nd Army: both of these corps have been erased from existence.
It has become apparent that the new leadership of the German 8th Army (von Hindenburg and Ludendorff) orchestrated the defeat of the 2nd Army by rapidly redeploying the I, I Reserve, and XVII Corps to face Samsonov and annihilate his force.
When von Francois' Corps, reinforced by a motley of Landwehr units and batallions from other divisions, struck Samsonov's left (I), the flank collapsed.  On his right, the VI failed to engage the enemy, retreating in near panic.  The bulk of the 2nd thus became trapped in a cauldron in the forests east of the village of Tannenberg.  The arrival of the 1st Army's II Corps was too little and too late.  Refusing to leave his army, Samsonov remained in command while encircled.  Utterly defeated and having issued the order for scattered units to disengage and retreat, Samsonov committed suicide while retreating with his staff.

The battle was a brilliant German victory:  Russia suffered 92,000 prisoners and over 30,000 casualties.  Ludendorff named the engagement after the village of Tannenberg in compensation for the defeat of Teutonic Knights by a Slavic alliance of Lithuanian, Polish, and Russian warriors in 1410 AD.
