At 5–7 kilometres (3.1–4.3 mi) in depth, the German defensive lines were deeper than the Soviets expected. The Soviet spearheads sustained heavy casualties but pushed through and in some areas achieved significant penetration.[17][18] The defenders were overwhelmed by the afternoon of the first day, with the 11th Guards Army advancing some 23 kilometres (14 mi). The German 5th Panzer Division attempted to fill the breach but they were met by the Russian supporting armour and were forced back.