The Soviets had enough warning of the German advance to ship grain, cattle, and railway cars across the Volga out of harm's way, but Stalin refused to evacuate the 400,000 civilian residents trapped in Stalingrad. This "harvest victory" left the city short of food even before the German attack began. Before the "Heer" reached the city itself, the "Luftwaffe" had cut off shipping on the Volga, vital for bringing supplies into the city. Between 25 and 31 July, 32 Soviet ships were sunk, with another nine crippled.