In February 1942, Heavy Artillery Unit (E) 672 reorganised and went on the march, and Schwerer Gustav began its long ride to the Crimea. The train carrying the gun was of 25 cars, a total length of 1.5 kilometres. 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 16 kilometres (9.9 mi) 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. 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. Five shells fired.
- 17 June
Fort Maxim Gorki and its coastal battery. 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 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.
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 from the city near the railway station of Taizy. The gun was fully operational when the attack was cancelled. The gun then spent the winter of 1942/43 near Leningrad.
The gun appears to have been destroyed to prevent its capture some time before 22 April 1945, when its ruins were discovered in a forest 15 kilometres (9.3 mi) north of Auerbach about 50 kilometres (31 mi) southwest of Chemnitz.
Dora was the second gun produced. It was deployed briefly against Stalingrad, where the gun arrived at its emplacement 15 kilometres (9.3 mi) to the west of the city sometime in mid-August 1942. It was ready to fire on 13 September. It was quickly withdrawn when Soviet encirclement threatened. When the Germans began their long retreat they took Dora with them. Dora was broken up before the end of the war, being discovered in the west by American troops some time after the discovery of Schwerer Gustav.
The Langer Gustav was a long cannon with 52 centimetre caliber and a 43 metre barrel. It was intended to fire super-long-range rocket projectiles weighing 680 kilograms to a range of 190 kilometres. This gave it the range to hit London from Calais, France. It was never completed after being damaged during construction by one of the many RAF bombing raids on Essen.
Landkreuzer P. 1500 Monster Project
The Monster was to be a 1,500 tonne mobile, self-propelled platform for an 80-cm K (E) gun, along with two 15 cm sFH 18 heavy howitzers, and multiple MG 151 autocannons normally used on combat aircraft. It was deemed impractical, and in 1943 was canceled by Albert Speer. It never left the drawing board and no progress was made. It would have surpassed the Panzer VIII Maus (heaviest tank ever built) and the Landkreuzer P. 1000 Ratte (never built) in weight and size.