Joseph Stalin's decision to delay the push toward Berlin from February to April has been a subject of some controversy among both the Soviet generals and military historians, with one side arguing that the Soviets had a chance of securing Berlin much quicker and with much lower losses in February, and the other arguing that the danger of leaving large German formations on the flanks could have resulted in a successful German counter-attack and prolonged the war further: the Germans did in fact mount a surprise counter-attack in Pomerania in mid-February, Operation Solstice. The delay did, however, allow the Soviets to occupy significant parts of Austria in the Vienna offensive.