Battle of Stallupönen The Battle of Stallupönen , fought between Russian and German armies on August 17 , 1914 , was the opening battle of World War I on the Eastern Front . It was a minor German success , but did little to upset the Russian timetable . Prelude . The German Schlieffen Plan was based on defeating France ( and the United Kingdom , should it be involved ) as quickly as possible in the west , which would then permit the Germans to transport their forces eastward to meet the massive Russian Army . The Russians were able to field up to ten complete armies compared to Germany ' s eight , but they were scattered across the country and would take some time to organize and move up . This meant that the Germans had a short window of time where they could fight a defensive battle , holding off what forces the Russians could move forward , while they waited for the battles in the west to be decided . Immediately prior to the opening of hostilities , the Eastern Front developed largely according to pre - war planning . Two Russian armies were in the immediate area , Pavel Rennenkampf ' s First Army east of the city of Königsberg , and Alexander Samsonov ' s Second Army to the south . Rennenkampf planned on marching on Königsberg , tying down any German forces in the area , while Samsonov would move northwest to cut off any escape . The Germans were also deployed largely according to everyone ' s expectations . The German Eighth Army was strung out in pockets in front of Rennenkampf , but did not have the manpower to completely cover the front of either of the Russian armies . On paper , the situation looked almost hopeless , and the standing orders were to fight a delaying retreat . However , Hermann von François , the commander of the First Corps of the German Eighth Army , was convinced his better - trained and equipped forces could halt , and perhaps defeat , Rennenkampf ' s Russian forces . Most of the Eighth Army was organized into a defensive line running south of Gumbinnen , about west of the Russian border . However , small units were sent forward to garrison towns , railway lines and strongpoints . They were ordered to retreat on contact with the enemy , joining the main forces at Gumbinnen . For the first five days of the war , the only combat was minor skirmishes with Rennenkampf ' s cavalry who were conducting reconnaissance along the border area . The battle . On August 17 , Rennenkampf started the invasion of East Prussia , marching the First Army directly westward towards the German lines . Although he faced no resistance , Rennenkampf stopped his advance in a neat line about five miles ( 8 km ) from the border . Acting without orders , François decided to take his forces to Stallupönen where one of the Russian divisions was resting . A furious frontal attack broke the Russian division , which fled eastward , losing 5 , 000 casualties and 3 , 000 prisoners , almost the entirety of the Russian 105th Regiment . When Prittwitz learned that François had engaged the Russians , he sent an adjutant to order François to break off the attack and retreat . François by this time was too committed to safely disengage , and had no intention of doing so anyway . He contemptuously , and famously , told the adjutant , " Report to General Prittwitz that General von François will withdraw when he has defeated the Russians . " Aftermath . While the Russians retreated , François pursued them into the evening , but ended his advance when he came under Russian artillery fire . He then reluctantly obeyed Prittwitz ' s order and withdrew 15 miles ( 24 km ) to the west , taking up new positions around Gumbinnen . His success was infectious , and convinced Prittwitz to be more aggressive in dealing with the Russian forces . This proved to be unwise at the following Battle of Gumbinnen two days later .