The Soviets had enough warning of the German attack to move all the city's grain, cattle, and railway cars across the Volga. But most civilian residents stayed in the city. The city lacked food even before the German attack. The "Luftwaffe" air attacks made the Soviets unable to use the River Volga to bring supplies into the city. Between 25 and 31 July, 32 Soviet ships were sunk in the River Volga.