In early 1915, the new German Chief of Staff, von Falkenhayn, switched reserves from the west to reinforce beleaguered Austro-Hungary. It was agreed that Austro-Hungary would now operate under German overall command. The newly unified armies achieved a decisive breakthrough in May with the Gorlice-Tranow offensive, proceeding to recapture Przemysl and then Lemberg, while a simultaneous advance was made in the north through the Russians’ Baltic territories. After pausing to allow resupply, the coordinated offensives resumed in the middle of July. The Russian High Command had hoped to maintain a makeshift defensive line along the Narew and Vistula rivers but, by this stage their forces were exhausted, demoralized, outnumbered and running short of supplies. Under the onslaught, the entire Russian front rapidly collapsed. By 15 August, Ivangorod and Warsaw had been taken and soon the whole of Poland, Lithuania and Latvia were in the hands of the Central Powers.