Although they were intended for World War II, they were not ready for action when the Wehrmacht outflanked the Maginot line by sweeping through the low country (Belgium) to start the Battle of France. However, they were ready in Autumn 1941, after the Wehrmacht invaded the Soviet Union (Operation Barbarossa). Gustav was used at the siege of Sevastopol in the summer of 1942. By the end of the siege on 4 July the city of Sevastopol lay in ruins, and 30,000 tons of artillery ammunition had been fired. Gustav had fired 48 rounds and worn out its original barrel, which had already fired around 250 rounds during testing and development. The gun was fitted with the spare barrel and the original was sent back to Krupp's factory in Essen for relining.