The Biggest Weapon Ever Built: Hitler’s Secret Gun — Schwerer Gustav D
5 June 1942, Sevastopol, the Soviet Union. An explosion arrives without warning. About sixteen kilometres behind the front, a massive railway gun has just fired, using a 32-metre barrel to launch a seven-tonne shell at a speed of roughly 720 metres per second. Operated by a crew of around 500 men, the weapon can strike its target located 25 km away in just 35 seconds.
At Sevastopol, one of the most heavily fortified positions in the Soviet Union, the shell penetrates metres of reinforced concrete before detonating, destroying gun emplacements and setting the position ablaze. At the firing site, the crew begins cleaning and cooling the barrel: an hour-long process before the next shot, which can destroy the strongest fortifications in the world. The name of this monstrous gun is Schwerer Gustav.
The origins of Schwerer Gustav or Heavy Gustav, lie in a problem that occupied German military planners for much of the early 1930s. Along its eastern border, France had constructed the Maginot Line which was a system of steel-reinforced concrete fortifications, underground tunnels, retractable artillery turrets, and interconnected strongpoints that was widely regarded as impenetrable to any existing weapon of that time.
The Line’s deepest forts were buried under tens of metres of reinforced concrete, their gun turrets encased in steel armour of a thickness that rendered them immune to conventional bombardment. In 1934, the German Army High Command secretly commissioned the Krupp firm of Essen to design a gun capable of destroying these fortifications from beyond the range of French counter-battery fire.
The requirements were precise and almost impossibly demanding: the weapon had to be able to punch through seven metres of reinforced concrete or one full metre of steel armour plate. Krupp’s engineer, Erich Müller, performed the calculations and arrived at specifications that strained the limits of industrial possibility.
The task would require a calibre of approximately 800 millimetres and a barrel at least thirty metres in length, and a projectile with a weight of around seven tonnes. A weapon matching these requirements would weigh over 1,000 tonnes when assembled, far exceeding the load capacity of any road bridge or conventional transport system. The only possible means of moving it would be on specially reinforced double railway tracks.
In March 1936, Adolf Hitler visited the Krupp factory in Essen and asked Gustav Krupp, the company’s senior director, what would be needed to breach the Maginot Line. Krupp was able to answer in detail. Hitler approved the project and construction was authorised in early 1937. Construction began at Krupp’s facilities in mid-1937, but forging the massive, complex barrel proved enormously difficult, and there were serious delays throughout the development process.
The Second World War began on 1 September 1939 when Nazi Germany invaded Poland. By late that year, a test model had been completed and sent to the Hillersleben proving ground near the city of Magdeburg, where an armour-piercing shell successfully penetrated the required seven metres of concrete and one metre of steel plate.
It was clear, however, that the gun would not meet Hitler’s March 1940 deadline. Acceptance trials for the completed weapon were eventually conducted in early 1941 at the Rügenwalde proving ground, now Darłowo in Poland, with Hitler in attendance. Alfried Krupp, the son of Gustav and by then one of the most important figures of the company, personally hosted the occasion.
Hitler, visibly impressed, allegedly referred to the weapon as ‘meine stählerne Faust’ – my steel fist. In keeping with Krupp company tradition, no payment was requested for the first gun. The second, which would cost 7 million Reichsmarks, was ordered alongside it. The gun was named Schwerer Gustav after the senior director of the firm, Gustav Krupp von Bohlen und Halbach.
The other gun of the same type was named Dora, after the wife of Erich Müller, the head of the Krupp design bureau. Given the complexity and high cost of manufacturing parts for these cannons, it remains a fact that these two cannons were likely never actually used in combat at the same time. The physical dimensions of the completed weapon were unlike anything in the history of artillery.
Fully assembled, Schwerer Gustav measured 47.3 metres in length and stood 11.6 metres tall. It sat on a specially designed carriage running on two parallel railway tracks, with a total of eighty wheels distributing its weight across the rails. The barrel alone was 32.5 metres long. The gun could fire a 4,800-kilogram high-explosive shell to a maximum range of 47 kilometres, or a 7,100-kilogram armour-piercing shell to a range of 38 kilometres.
The rate of fire was approximately one round every thirty to forty-five minutes under sustained operations, limited by the need to swab and cool the barrel after each discharge. Loading was a complex and complicated process: shells were delivered by rail to the rear of the gun, hoisted by cranes to the firing deck, and loaded by hydraulic ram.
Operating the gun at full capacity required a crew of 500 men and weeks of preparatory work including thousands of workers and soldiers. There was one fundamental irony at the heart of the weapon’s existence. Schwerer Gustav had been designed specifically to destroy the Maginot Line, but when the Battle of France began in May 1940, the gun was not ready.
Nor, as it turned out, was it needed – rather than attacking the Maginot Line directly, German armoured columns swept through the Ardennes, bypassed the entire fortification system, and drove deep into France. The Maginot Line’s garrisons were cut off and eventually surrendered without the fortifications having been seriously attacked. France fell in June 1940 and the weapon that had consumed years of industrial effort and nearly incalculable resources had been rendered irrelevant before firing a single shot.
Many senior officers in the Wehrmacht, the German armed forces, regarded it as an expensive folly and argued that the resources could have been better spent elsewhere. Hitler overruled them and insisted that development continue. The gun was, in some way, his personal project, and he was determined that a use would be found for it. After Nazi Germany invaded the Soviet Union on 22 June 1941, the opportunity arose for the Schwerer Gustav as well.
Sevastopol, the great naval fortress on the Crimean Peninsula and the home port of the Soviet Black Sea Fleet, was one of the most formidable defensive positions in the world. German and Romanian forces reached Crimea in autumn 1941 and overran most of the peninsula, but Sevastopol held. Its garrison repelled repeated assaults through the winter of 1941 and into 1942 with extraordinary tenacity.
The city’s fortifications were layered, extensive, and deep and attacking it required the most powerful siege artillery Germany possessed. On 8 January 1942, Heavy Artillery Unit 672 was formally established with 1,420 men under the command of Robert Böhm, with the specific purpose of deploying Schwerer Gustav against Sevastopol. In February 1942, the unit began the long journey south to Crimea.
The train transporting the gun consisted of twenty-five cars and stretched 1,5 kilometres in total length. The assembly of the weapon began in early May 1942. By 5 June, after five weeks of preparation involving thousands of men, Schwerer Gustav was ready to fire. The gun’s combat record at Sevastopol was concentrated and technically remarkable, though strategically modest.
On 5 June, it fired eight armour-piercing shells at Soviet coastal gun batteries at a range of 25 kilometres, and a further six at Fort Stalin. Seven shells followed at Fort Molotov on the next day. The most extraordinary moment came when nine shells were directed at a target known as White Cliff, an underground Soviet ammunition depot buried approximately thirty metres below the surface of the water.
It was the ninth shell that found it: an armour-piercing round that penetrated through rock and seawater before detonating inside the depot, producing an explosion that shook the entire bay, destroyed the Soviet supply infrastructure to the northern port fortifications, and sent up a column of debris and smoke visible from the German lines kilometres away. 
By the time the siege ended on 4 July 1942 and the city fell, Schwerer Gustav had fired 47 rounds in total. It had worn out its original barrel, which had already been used for approximately 250 test rounds during development. The spent barrel was shipped back to the Krupp factory in Essen for relining, and a spare was fitted.
The gun was then dismantled and moved north, to the Leningrad front, where a major assault on the city was being planned. It was positioned approximately thirty kilometres from Leningrad, near the railway station of Taytsy near the town Gatchina, and declared fully operational. The planned offensive was then cancelled, leaving Schwerer Gustav assembled and ready near a city it would never fire upon.
It spent the winter of 1942 and into 1943 in the north before being returned to Germany for refurbishment. The second gun – Dora, had meanwhile been transported to Stalingrad in August 1942, arriving at an emplacement fifteen kilometres west of the city and declared ready to fire on 13 September. Sources differ regarding its operational deployment, and according to some, it was not used during the fighting, because before it could engage in the battle, the threat of Soviet encirclement, forced a hasty withdrawal. According to this theory the Dora was loaded back onto its rail transporter and taken west without having fired a single round in combat. Its entire operational career lasted less than a month and produced nothing.
Schwerer Gustav was refurbished and later considered for deployment against the Warsaw Uprising of 1944, but the uprising was crushed by other means before the gun could be brought to readiness. It played no role in that operation, though its presence in Germany during this period led some later sources to confuse it with the heavy siege mortars, Karl-Gerät weapons of the 600-millimetre class, that were actually used against the city.
By early 1945, with forces of Western Allies advancing from the west and Soviet armies closing from the east, the weapon had become a liability. Too large to conceal, too slow to move, and impossible to protect from air attack during assembly, it could not be defended and could not be hidden. On 14 April 1945, one day before American troops arrived, German personnel destroyed the gun with explosives to prevent its capture.
Its ruins were discovered on 22 April 1945 by American soldiers in a forest fifteen kilometres north of Auerbach in eastern Germany, close to today’s border with Czech Republic. In the summer of 1945, Soviet specialists were brought to examine the wreckage. In the autumn, the remains were transferred to Merseburg, where the Soviets were collecting captured German military material for study.
The second Schwerer Gustav or Dora met a similar end: it was moved to Grafenwöhr, a town in eastern Bavaria and destroyed there on 19 April 1945. Its debris was discovered separately by American troops and eventually scrapped in the 1950s. Schwerer Gustav was, by any technical measure, the largest rifled weapon ever built and the heaviest mobile artillery piece in the history of warfare. It was also a strategic failure measured against the resources it consumed.
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