672 reorganised and went on the march, and Schwerer Gustav began its long ride to Crimea. The train carrying the gun was of 25 cars, a total length of 1.5 kilometres (0.9 mi). The gun reached the Perekop Isthmus in early March 1942, where it was held until early April. The Germans built a special railway spur line to the Simferopol-Sevastopol railway north of the target. At the end of the spur, they built four semi-circular tracks especially for the Gustav to traverse. Outer tracks were required for the cranes that assembled Gustav. The siege of Sevastopol was the gun's first combat test. 4,000 men and five weeks were needed to get the gun into firing position; 500 men were needed to fire it. Installation began in early May, and by 5 June the gun was ready to fire. The following targets were engaged: 5 June Coastal guns at a range of 25,000 m. Eight shells fired. Fort Stalin. Six shells fired. 6 June Fort Molotov. Seven shells fired. "White Cliff" also known as "Ammunition Mountain": an undersea ammunition magazine in Severnaya ("Northern") Bay. The magazine was sited 30 metres under the sea with at least 10 metres of concrete protection. After nine shells were fired, the magazine was ruined and one of the boats in the bay sunk. 7 June Firing in support of an infantry attack on Südwestspitze, an outlying fortification. Seven shells fired. 11 June Fort Siberia knocked out of action. Five shells fired. 17 June Maxim Gorky Fortresses bombarded. Five shells fired. 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 47 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. The gun was then dismantled and moved to the northern part of the eastern front, where an attack was planned on Leningrad. The gun was placed 30 km (18.6 mi) from the city near the railway station of Taytsy. The gun was fully operational when the attack was cancelled. The gun then spent the winter of 1942/43 near Leningrad. Dora Dora was the second gun produced. It was deployed briefly against Stalingrad, where the gun arrived