Although Poland managed to achieve victory and push back the Russians, Piłsudski's plan to outmanoeuvre and surround the Red Army did not succeed completely. On July 4, four Soviet armies of the North-Western Front began to advance on Warsaw. After initial successes, by the end of August, three of them—the 4th, 15th and 16th Armies, as well as the bulk of Bzhishkyan's 3rd Cavalry Corps—had all but disintegrated, their remnants either taken prisoner or briefly interned after crossing the border into German East Prussia. The 3rd Army was the least affected; due to the speed of its retreat, the pursuing Polish troops could not catch up with it.