German Reich (1941-1945)
Self-Propelled Super-Heavy Mortar – 7 Built
Throughout the history of warfare, fortifications have always posed significant challenges for attacking armies. These strongholds often necessitated intense and prolonged sieges, draining resources, costing numerous lives, and consuming a great deal of time. Even with advancements in military technology, early twentieth-century fortifications remained nearly impregnable. However, during the early stages of the First World War, the Germans demonstrated that super-heavy siege artillery could effectively breach these defenses, indicating that traditional fortifications were no longer as formidable as they once were. By the onset of the Second World War, the effectiveness of large-caliber artillery and mortars in breaching fortifications had not been forgotten by the Germans. To tackle the formidable French Maginot Line, in 1935, the Germans initiated the development of seven super-heavy mortars mounted on self-propelled chassis. This led to the creation of the so-called Karl-Gerät 040 and 041, showcasing a significant evolution in siege weaponry.
Origin in the First World War
In the years leading up to the First World War, the German Army foresaw that a major conflict was inevitable. One of the primary threats was the combined might of the Russian Empire and France. To counter the vast manpower of Russia and avoid the peril of fighting on two fronts, Germany planned to quickly defeat France first. Achieving this required neutralizing numerous Western fortifications without the delay of prolonged sieges. Their solution was to develop super-heavy artillery capable of bombarding these fortifications into submission.
One such weapon was the massive 42 cm howitzer, commonly known as Big Bertha. This artillery piece played a crucial role in quickly overcoming many Belgian fortifications after just a few days of fighting. The success of Big Bertha demonstrated that even heavily protected and entrenched fortifications were vulnerable to large-caliber artillery rounds.
In addition to their massive siege guns, the Germans also deployed smaller yet still large-caliber mortars. These mortars, including the 25 cm schwerer Minenwerfer (Eng. Heavy mortar), operated much closer to enemy lines, due to their limited range. Muzzle-fed and fired from static, dug-in emplacements, these weapons, despite their relatively small size and range, proved highly effective. The large payloads they delivered were particularly successful in destroying enemy-entrenched positions, leading to their widespread use during the First World War.
After the war, the German Army was subjected to strict prohibitions on developing new military technologies under the Treaty of Versailles. This included a ban on the development of large-caliber artillery. The Western powers hoped to cripple Germany with the harsh conditions of the peace treaty. However, in reality, these measures fostered resentment among the German population, ultimately setting the stage for the next great war.
Development History of a New Super-Heavy Artillery System
The effectiveness of large caliber guns and mortars against well-dig in fortification was not lost to the Germans. They understood that, at some point, they would have to confront the French once again, who were shielded by the massive and formidable Maginot Line. This line was considered the best-fortified bastion in the world at the time. Ordinary artillery, even of larger calibers, would have little impact against the thick concrete bunkers embedded in the ground. Therefore, the Germans recognized the necessity of developing super-heavy artillery or mortars to overcome these formidable defenses.
With the rise of Nazism in Germany, the German Army underwent a massive expansion, which included significant investments in new weapons and technological advancements. By 1935, the German Army felt confident enough to begin developing a weapon capable of breaching the Maginot Line. That year, they turned to Rheinmetall to design such a weapon. The first preliminary drawings and calculations were submitted to the Waffenamt (Eng. German Army Weapons Agency) in March 1936. To tackle the Maginot Line, Rheinmetall engineers proposed an 80 cm caliber mortar.
This mortar was designed to be operated from a static emplacement, which required it to be dug into the ground. Essentially, it was a massive installation that needed to be transported in small components and assembled on-site. The estimated range of the mortar was 1 km when firing a 4-tonne round, and 2 km when firing a lighter 2-tonne round.
After thoroughly analyzing Rheinmetall’s proposal, the Waffenamt issued a formal request with precise performance specifications in October 1936. They deemed the maximum range of 2 km as insufficient. Given the mortar’s size and the time required for its assembly, this range would leave the crew significantly exposed. Therefore, the Waffenamt requested the use of a lighter 2-tonne round, setting the maximum range at 3 km. The entire assembly was to be transported in parts and then fully assembled using a specially designed crane, with the assembly process not exceeding 6 hours. Additionally, the mortar was to be muzzle-loaded, a decision undoubtedly influenced by the mortars used in the trenches during the First World War.
At the start of 1937, Rheinmetall proposed reducing the caliber to 60 cm, with a maximum elevation estimated to reach up to 120°, and a total weight of 55 tonnes. To transport the heavy mortar, it would need to be disassembled into smaller components, each weighing around 9 tonnes. Each of these components would require a separate towing vehicle. Rheinmetall engineers realized that assembling the entire mortar would take more than the initially requested 6 hours. Therefore, they proposed a more efficient solution: mounting the mortar assembly on a fully tracked, self-propelled chassis. This offered several advantages. For instance, the mortar could be ready for action in less than 30 minutes, eliminating the need for multiple support vehicles to tow its components. If necessary, the entire vehicle could still be disassembled into smaller components. Additionally, there was no need to dig up the ground to place the mortar, as the self-propelled chassis was designed to be lowered to the ground before firing. Coupled with a hydraulic carriage recoil mechanism, this design would greatly reduce the immense recoil force.
In October 1937, further changes were implemented. The muzzle-loading system was abandoned, as it would have impeded the mortar’s accuracy. The driver’s compartment was repositioned to the rear of the self-propelled chassis. Essentially, the entire chassis was driven in the opposite direction from the main armament. This configuration allowed for quick movement of the vehicle if it was in danger, as the driver did not have to make a large turn to reach safety. Rheinmetall engineers also calculated that the maximum firing range could be increased to 4 km. The estimated total weight of the vehicle was to reach 97 tonnes.
In March 1938, a meeting between Rheinmetall and Waffenamt officials was held. During that meeting, it was agreed that Rheinmetall would begin working on construction drawings. In addition, upon special insistence by General Karl Heinrich Emil Becker, who was in charge of Wa Prw 4 (Eng. German Army’s Ordnance Department office responsible for designing artillery, later renamed to Wa Prüf 4), beside the prototype, six more vehicles were to be built. Given its specialized role and extensive cost, Rheinmetall was informed that no further production orders would be given.
As the work on the project progressed, there was a huge concern about the chassis’ ground pressure and mobility, given the extensive weight. At that time, the German tanks that were in service did not have greater ground pressure than 0.68 kg/cm2, in the case of the Panzer IV Ausf.A. This was new territory for the Germans, as they did not know how the new vehicle, with such weight, would behave while driving. To gain some clues, they used one Neubaufahrzeug (Eng. New Construction Vehicle) as a test vehicle. This was a German attempt to develop a multi-turret tank, of which only 5 were built, before the project was canceled. On its superstructure, extra weight was added until it reached a ground pressure of 1.43 kg/cm2. The driving trials were conducted on various ground types and none proved to be problematic for the test vehicle.
With this problem sorted, another challenge emerged: German engineers needed to determine whether the extended track contact length would impact steering. To investigate this, they developed and constructed a small-scale remote-controlled test model at 1/10 scale. Following extensive testing across diverse terrains, they found no significant issues affecting its performance.
With the chassis problem resolved, the next step was to build the first working prototype. In order to test the weapon design and various types of ammunition, General Karl Becker requested Rheinmetall to construct a fixed concrete mount for the mortar, which would serve as a firing test bed. This contraption was designated Anschiesslafatte I (Eng. Shooting Carriage I). Once completed, it underwent testing at the Hillersleben evaluation and testing center. In this setup, the mortar could traverse 10° in both directions and had an elevation range of 0° to 75°. The entire assembly, including the mortar and concrete mount, weighed nearly 160 tonnes. Due to its classified status as a secret weapon, a special wooden mock-up warehouse could be constructed around it to conceal it from the Allies when not in use. During test firing, a recoil length of 1 meter was observed, with a braking pressure of approximately 450 tonnes. This recoil length exceeded the German’s initial prediction of 50 cm. Further firing trials were conducted to assess barrel service life and test different types of ammunition, yielding valuable data that contributed to understanding the mortar’s overall firing performance.
To facilitate further studies, Rheinmetall developed an improved Anschiesslafatte II mount base in November 1939. This mount was specifically designed to test the barrel’s recoil. The elevation range was adjusted from 55° to 75°.
Field testing of the self-propelled chassis took place in May 1940 at Unterlüss. Since the mortar was not yet installed, ballast was used to simulate its weight. The first fully completed vehicle was presented to the Army on 2nd July, 1940.
Designation
During its development and service history, the precise designation of this vehicle changed numerous times. This was a common occurrence for many German military vehicles that saw service during the Second World War. The reasons for these changes included bureaucratic confusion, the desire for a more imposing name, and shifts in the vehicle’s purpose, among other factors.
In its early development stage, Rheinmetall simply designated it as Project 4. In November 1940, it was renamed Gerät (Eng. Device or Equipment) 040. By February 1941, the well-known nickname Gerät-Karl was used for the first time. In July 1942, the name was turned around to Karl-Gerät, which remained in use until the end of the war. The name Karl referred to General Karl Emil Becker, who played a significant role in the project. Although he committed suicide in April 1940, the German Army decided to honor him by naming the vehicle after him. For simplicity, this article will refer to the self propelled mortar as Karl.
Additionally, each of the seven vehicles received a military Ausführung (Eng. Version or type) designation. Instead of the more standard letter designation, they were marked with Arabic numerals. Each vehicle, except the last one, was also given a nickname inspired by mythological figures and Nordic gods. These names were usually painted in black or white on the sides of the large mortar housing.
| Gerät number | Ausf. | Nickname |
|---|---|---|
| Number I | 1 | Adam* |
| Number II | 2 | Eva** |
| Number III | 3 | Odin |
| Number IV | 3*** | Thor |
| Number V | 4 | Loki |
| Number VI | 5 | Ziu |
| Number VII | 6**** |
* Renamed to Baldur near the end of the war
**Renamed to Wotan near the end of the war
*** It is unclear why these two received the same Ausf. destination number
**** It is assumed that the last vehicle was marked as Ausf.6, but it is not completely clear
Source: T.L. Jentz and H.L. Doyle Panzer Tracts No. Bertha’s Big Brother Karl-Geraet
Production
Only seven vehicles were ordered. These were delivered after a firing test series. It is important to note that the last vehicle was mainly issued for various tests and evaluation purposes.
| Gerät number | Date of acceptance after firing trials |
|---|---|
| Number I | 5th November 1940 |
| Number II | 7th November 1940 |
| Number III | 20th February 1941 |
| Number IV | 17th April 1941 |
| Number V | 11th June 1941 |
| Number VI | 28th August 1941 |
| Number VII | Unknown, possibly in 1942 |
Design
Chassis
Despite its immense and imposing size, the Karl’s box-shaped chassis had a rather simple overall design with not much going inside it. Essentially it could be divided into three major components. The lowering mechanism was positioned in the front part of the vehicle chassis. Most of the middle part was actually empty. It was to serve as a base for the mortar and its carriage. Lastly, to the rear, the engine with the transmission and the driver compartments were located.
The whole construction consisted of metal plates that were welded together. The front part of the chassis was covered with a simple box-shaped cover. To provide access for the crew, two metal ladders were installed. The front wall of this compartment also served as a storage area for the crew’s various tools.
The enclosed engine compartment acted as a working platform for the crew. On both sides of the engine compartment, two large exhaust pipes were installed. To gain access to the engine, a few inspection hatches were installed, in addition to single metal ladders. On the right side of the engine compartment, there was a small indentation where the driver was seated. It was a square-shaped hole, with a seat and driving controls under it. To provide more working room, on its sides, a folding platform was installed. Overall, the vehicle had a huge size with a length of 11.15 m, width of 3.16 m, and height of 2.72 m.
Engine
Despite the limited production run, these vehicles were powered by two different engines, both developed by Daimler-Benz, which also produced all engines used in German tanks. Rheinmetall ordered four MB 503A gasoline engines, which were installed in the I, II, VI, and VII vehicles. The remaining three vehicles were equipped with MB 507C diesel engines. The reason for the use of two different engine types remains unclear. In 1944, Daimler-Benz delivered four additional MB 507C diesel engines, which were used to replace the MB 503A gasoline engines.
Both engines had a power output of 580 hp at 1,850 rpm. With a total weight of 124 tonnes, the maximum speed was 10 km/h for the gasoline engine and 6 km/h for the diesel engine. The fuel load consisted of 1,200 liters, providing an effective range of 42 km for the gasoline engine and 60 km for the diesel engine. Fuel consumption per hour was 175 liters for the gasoline engine and 120 liters for the diesel engine.
Vehicles I, III, IV, and VII were equipped with a three-speed forward and one-speed reverse transmission designed by Ardelt. In contrast, the remaining three vehicles (II, V, and VI) utilized a two-speed forward and one-speed reverse transmission with a Voith TG 504 hydraulic drive. Some sources indicate that Vehicle VII may also have been fitted with the Voith TG 504 transmission instead. Since the last vehicle was used for various testing and evaluation purposes, it is possible that its original transmission was replaced at some point.
Despite the immense weight, the Germans did not experience significant difficulties during off-road driving. Before crossing muddy terrain or ditches, these were covered with planks or whatever materials were available. Due to its considerable length, the driver had to pay particular attention to the terrain to avoid accidentally going off track or, in the worst-case scenario, bogging down the entire vehicle.
Suspension
Two types of torsion bar suspension were employed. The first two vehicles used eight rubber-rimmed wheels. In addition, there was a rear-mounted drive sprocket, front idler, and eight return rollers. The drive sprocket had 17 teeth and used a 170 mm wide pitch track. The torsion bars were 2.5 m long.
The remaining vehicles were equipped with eleven all-steel road wheels. Although the positions of the idler and drive sprocket remained unchanged, the number of return rollers was reduced to six. The drive sprocket was redesigned with twelve teeth and a 240 mm wide pitch track. Additionally, the torsion bar length was slightly reduced to 2.11 meters. Later in the war, the first two vehicles also received this updated suspension system.
When preparing for firing, the entire vehicle was lowered to the ground using engine power. Despite its weight and size, this process took only 15 seconds. Raising the vehicle for movement also took just 15 seconds. This capability made changing the firing position relatively easy, despite the vehicle’s limited traverse. The first model, however, did not have this mechanism when it was introduced in 1941. Instead, the crew had to manually lower or raise the vehicle using cranks.
Armament
The Karl’s main armament consisted of a 60 cm caliber mortar with a relatively short barrel, measuring 5.07 meters. It was loaded using a large sliding breech. The mortar was encased in a large box-shaped housing that contained four recoil cylinders and had to withstand a braking pressure of approximately 680 tonnes. The elevation range of this mortar was from 0° to 70°, but it could only fire at elevations between 55° and 70°. The traverse was limited to 4° in both directions. To engage targets outside this traverse angle, the entire vehicle had to be repositioned. The elevation and traverse hand wheels were located on the left side of the mortar housing.
To manage the immense recoil force and maintain accuracy, a secondary recoil mechanism was installed inside the heavy mortar carriage. Similar systems were used on the 17 cm K 18 gun and the 21 cm Mrs howitzer, which shared the same carriage. Essentially, this meant that, during firing, the entire carriage would recoil back approximately 78 cm. The mortar’s own recoil length was 98 cm. The carriage recoil cylinders could sustain up to 104 tonnes of pressure.
The first round of ammunition developed for this vehicle was a high-explosive round containing 600 kg of explosives, but it never entered production. Instead, the schwere Betongranate (Eng. Heavy Concrete Penetrating Shell) was the first to be introduced into service. This round measured 2.51 m in length and weighed 2.17 tonnes, with an explosive charge of 280 kg. Depending on the number of charges used (either 1 or 4), it had a maximum firing range of 4.32 km and a minimum range of 2.84 km, with a muzzle velocity of 220 m/s. Due to its weight and speed, it could penetrate 2.5 m of reinforced concrete before detonating.
Despite its effectiveness, the range of the schwere Betongranate was considered too short. Therefore, in 1942, a lighter round, known as the leichte Betongranate (Eng. Light Concrete Penetrating Shell), was introduced. This round weighed 1.7 tonnes and carried a 220 kg explosive charge. By using more charges (5 to 9) and taking advantage of its lighter weight, its muzzle velocity was increased to 283 m/s, extending its range to 6.64 km.
Due to the weight of the rounds, manual loading was not feasible, necessitating the use of an electrically (or, when needed, manually) driven rammer, and a loading platform. After each shot, the mortar had to be lowered to 0°. A well-trained crew could maintain a firing rate of one round every 10 minutes. Before each shot, one crew member had to inspect the barrel for any cracks or damage to its 112 rifling grooves.
Crew
The crew of this vehicle comprised 21 men: a commander, 18 gunners, a driver, and an assistant driver. The driver was seated in his compartment, with the assistant directly behind him. The rest of the crew was positioned around the mortar, performing various tasks, such as setting the angle of fire and loading the large rounds.
Munitionsschlepper Auf Panzer IV
Transporting and loading the massive shells was a complex task, requiring specialized equipment and vehicles. While half-tracks were typically used for such operations, they were deemed insufficient for the Karls. Consequently, the Germans repurposed the Panzer IV chassis for this. At least 13 different Panzer IV chassis (from Ausf.D to F) were reused for the project. The modifications included removing the turret and adding a new superstructure. Additionally, a sufficiently strong electrically powered crane was installed, and a storage bin for four rounds was added to the rear. Typically, two such vehicles were allocated to each Karl vehicle. That changed depending on the combat needs and situation.
Transportation
The Karl vehicles could be transported in various ways. For short distances, they used their self-propelled chassis to move to their designated firing positions. Despite its size, the Karl offered relatively good overall driving performance. However, precautions were necessary to avoid potentially bogging down in mud or rough terrain, as evacuating such a heavy vehicle would surely be a formidable task. To the author’s knowledge, there has been no reported instance of this actually occurring.
In November 1940, concerns arose regarding the ability of the vehicle to traverse bridges due to its considerable weight when fully assembled. There was a fear that the vehicle might be too heavy for many bridges, risking their structural integrity. Consequently, Rheinmetall was tasked with designing special auxiliary transport trailers, which featured multiple axles and a low-slung profile. These trailers were intended to support the vehicle by distributing its weight more effectively. To address the issue, the vehicle would first be stripped of many of its heavier components. With the aid of these specially designed trailers, it could then use its own power to safely cross bridges that might otherwise be too fragile to support its weight.
For longer distances, rail transport was employed. Due to the vehicle’s immense weight, it could not be transported on a standard rail wagon. Instead, Linke-Hofmann from Breslau developed specialized rail equipment. It consisted of two five-axle carriages and a rising crane. These would be connected to pintle connection points on the Karls and then the vehicle would be raised by two hydraulic props.
The 54 cm Armed Variant
The 60 cm mortar, despite its tremendous destructive power, lacked sufficient range. Hitler raised this concern and requested the development of a new 54 cm caliber mortar that could be mounted on existing vehicles. Although the project began in February 1941, it faced significant delays due to various mechanical problems. The delivery of three such vehicles commenced only in June 1944, with Vehicles I, III, and V being equipped with the new armament. However, their combat use was limited, as they were only deployed near the end of the war. The new mortar’s greater muzzle velocity extended its maximum firing range to 10 km.
Organization
The first two vehicles were delivered in November 1940, which was too late for them to be used against the French Maginot Line. Ironically, the primary objective for which they were designed was accomplished without their involvement. Nevertheless, work on the remaining Karl vehicles continued and was not canceled.
At the beginning of 1941, Batterie (Eng. Battery) 833 was established and stationed at the Bergen proving grounds, where the necessary crew training was conducted. In April 1941, a new unit, schwere Artillerie Abteilung 833 (Eng. Heavy Artillery Battalion), was formed. This battalion comprised a command battery and the 1st and 2nd batteries, each equipped with two vehicles. Vehicles No.I and II were assigned to the 1st Battery, while Vehicles III and IV were assigned to the 2nd Battery. The original 833rd Battery became the 1st Battery of this newly formed battalion.
The command battery did not have any Karl vehicles at its disposal. Instead, it was equipped with radio and telephone communication equipment. Each of the two batteries was supported by 14 motorcycles, two of which were equipped with sidecars, 5 passenger and off-road cars, two communication vehicles, 8 Sd. Kfz.8 half-track, and, lastly, four ammunition Panzer IVs. In total, each battery had 160 men and officers.
Combat
In anticipation of the invasion of the Soviet Union, the 833rd Heavy Artillery Battalion was integrated into German preparations. The 1st Battery, equipped with 60 spare rounds, was attached to the 17th Army, while the 2nd Battery, with 36 rounds, supported the 4th Army. When the war broke out in June 1941, the 1st Battery was assigned to bomb Soviet positions at Wielki Dział in Poland. The 295th Infantry Division, supported by two Karl vehicles, was tasked with capturing this fortified position. On 23rd June 1941, the German infantry successfully stormed the Soviet defenses and took the position. Vehicle No.I was reported to have fired only four rounds. The second vehicle did not even reach its destination, as its track broke down and it was unable to participate in the engagement. On the 23rd of June, both were reported to be non-operational due to malfunctions and were sent back to Germany.
The 2nd Battery was assigned to bombard the Soviet fortifications at Brest-Litovsk. These were not new concrete fortifications, but rather old brick or earthwork structures. During the preparation for engagement, the assembly crane was damaged. On June 20th, the necessary replacement parts were airlifted. Once repairs were completed, the two Karl mortars commenced bombardment on 22nd June 1941. After a brief period of combat, an urgent report was sent to Berlin. It stated that, after firing only a few rounds, the mortars became stuck in the bore. This caused significant concern for the entire Karl project due to the substantial resources and time invested. Consequently, a delegation led by Oberst Gallwitz was dispatched to investigate. To their surprise, it was found that the two Karls from the 2nd Battery had fired nearly all their available ammunition without major issues. There were a few instances where a round could not be fired, requiring the crew to use winches from the Sd.Kfz.8 halftracks. The investigation revealed that there was no issue with the Karl mortars themselves; instead, the problem lay with the poor quality of the copper driving bands on some rounds. Between 22nd and 24th June, 31 rounds were successfully fired, while three of the remaining five rounds were reported as unusable. The origin of the false rumor about the Karls’ malfunction is unclear.
The first combat action of the two Karls was highly successful. There were no major issues with the vehicles, including both the chassis and the mortar. Although there were some minor problems during rail disembarking, these were not significant. It was also observed that the rounds landed relatively close to each other, indicating a high level of precision. While there were no modern fortifications present, sections of thick-walled fortifications were completely obliterated. A 2-meter thick brick wall was effortlessly destroyed, something that other German heavy artillery had been unable to achieve. A direct hit from the 60 cm round created a crater 10 m deep and 30 m wide, accompanied by a dust cloud 300 m wide and 170 m high. Two rounds were recorded as duds and had to be dug out and disarmed. Overall, the first combat action of the Karls was promising.
Following this success, the four Karls and their crews were sent back to Germany. The 833rd Battalion was reequipped with 21 cm Mörser 18 artillery and redeployed to the Eastern Front in August 1941.
By August 1941, all four vehicles were sent back to Rheinmetall for repairs and maintenance. During their return, one Karl vehicle was redirected to the town of Terespol in Eastern Poland on the personal order of Adolf Hitler. Hitler and Benito Mussolini were on an inspection tour across Poland, and Hitler was keen to show the captured Soviet fortifications. Additionally, he wanted to demonstrate the Karl vehicle to Mussolini. Despite Hitler’s insistence on firing a round, the vehicle was damaged and unable to do so.
Breaking Sevastopol
In early 1942, the Germans undertook extensive preparations to amass their heaviest artillery for a crucial offensive against the heavily fortified Soviet defenses surrounding the port city of Sevastopol. In 1941, General Erich von Manstein failed to capture the city due to insufficient manpower and equipment. To remedy this, the Germans deployed their most formidable weapons, including the colossal 80 cm Dora railway gun and the Karl vehicles.
The 833rd Battalion was ordered to provide manpower for a new battery equipped with three Karl vehicles (Vehicles No.II, III, and IV). This unit, designated simply as Karl Battery, was to be placed under the command of the 11th Army. Due to the limited range of the Karl vehicles, special dug-out positions were required. Work on these positions began in April 1942. Each position was to be 15 m long, 10 m wide, and 3 deep. A group of 80 to 100 men was tasked with this extensive excavation, which was estimated to take 90 days to complete. To avoid detection by the enemy, all excavation work was conducted at night.
The Karl Battery reached the frontline in late May 1942. The vehicles were unloaded from trains, disassembled into pieces, and transported near their final destination for reassembly. The last 3.5 kilometers were traversed under their own power. To protect against enemy air spotters, the Germans employed heavier fighter escorts, which also helped to somewhat mask the sound of the Karl’s engines. Their designated targets were Fort No. 30 and Sevastopol Fort No. 39, known as Bastion. Fort No. 30 featured two twin 30.5 cm caliber guns housed in a massive turret protected by 20 to 30 cm of plate armor.
The bombardment began on June 2 and lasted until 13th June 1941, when the last round was spent. During this period, 72 heavy and 50 light rounds were fired. Additional rounds were dispatched at the end of June, with 50 light rounds being fired on June 30 and 25 heavy rounds on July 1. After the 19th of July, the three vehicles were sent to the rear for recuperation and necessary maintenance.
Some sections of the Sevastopol defense bastions proved immune even to the 60 cm rounds. However, on many occasions, the Karl rounds caused significant damage. One of the defending Maxim Gorki turrets was obliterated by a direct hit. Sections of the so-called Bastion’s thick and sloped wall, approximately 30 meters wide, were completely destroyed. Interestingly, one 60 cm round ricocheted off the Maxim Gorki fortress and flew several hundred meters away. After a few days of searching, it was recovered by the Soviets and sent to Moscow for evaluation.
Interrogation of the captured defenders later revealed that the heavy artillery and even Ju 87 bombs had minimal impact on them. However, the 60 cm rounds generated massive shockwaves that significantly demoralized the defenders.
Attempts to Take Leningrad
In July 1942, an order was issued to form a new unit, designated as the 628th Battery. This unit was to consist of two vehicles, with manpower drawn from the 833rd Battalion. The number of vehicles was later increased to three, with one held in reserve. The 628th Battery was intended to support the German effort to capture Leningrad in late 1942. However, a Soviet counter-attack in the area effectively halted any German attempts to seize Leningrad. As a result, the Karls were never used against the Soviets on this part of the front. The 628th Battery remained on the Eastern Front until it was recalled to Germany in December 1942.
In May 1943, new structural changes were implemented. The 628th Heavy Artillery Battalion was to be formed, consisting of two batteries with a total of five vehicles. The 628th Battery was incorporated as the 1st Battery of this new battalion. By July 1943, it was part of Army Group North, with the Germans still harboring hopes of capturing Leningrad. However, by August 1943, it became clear that this was no longer possible due to the German defeat at Kursk and the subsequent Soviet counterattack. They may have seen some action against the Soviet position at Izyum in Ukraine during the summer of 1943. By September 1943, the unit was reequipped with 21 cm mortars, and the Karls were sent back to Germany.
The Karls were allocated to a new unit, designated as Kommando für Karl-Geräte (Eng. Command for Karl devices) in September 1943. This, in turn, was renamed in June 1944 to Kommando für Sonder-Gerät des schwere Artillerie Abteilung 628 (Eng. Command for special devices of the heavy artillery battalion).
Against Warsaw in 1944
After 1943, the Germans began a gradual retreat on all fronts, resulting in the Karls being largely inactive throughout much of 1944. However, the situation shifted dramatically with the outbreak of the Polish uprising in Warsaw on 1st August 1944. In response to this uprising, a new German unit, designated Heeres Artillerie Batterie 638 (Eng. German Army Artillery Battery), was hastily formed on the 14th August 1944. They prepared a stockpile of 250 60 cm rounds in anticipation for the upcoming operation. The first vehicle, No.VI Ziu, arrived near Warsaw on the 17th of August 1944.
The Karl mortar was initially positioned in Wolski Park to engage Polish defenders. Before this, the Germans had constructed specialized concrete platforms at strategic locations throughout Warsaw. The initial target of the Karl vehicle was the Old Town and the city center. Despite its formidable 60 cm caliber, the Karl mortar did not utilize explosive rounds, which somewhat limited its destructive capabilities. Often, its rounds simply passed through large buildings, causing significant damage, but not destroying them completely. Occasionally, rounds failed to detonate and had to be disarmed. On August 18th, one such round struck the Polish hotel Adria, prompting efforts by Polish personnel, even utilizing German prisoners, to disarm it despite lacking proper equipment. This process extended into August 19th before success was achieved. The explosive salvaged from disarmed rounds was used to create improvised hand grenades. The unexploded round remained in the hotel until 1965, when it was finally excavated and relocated to the Polish Military Museum in Warsaw. A few more rounds were found in the following years, which had to be disarmed. The last one was found in 2007!
Overall, the Germans considered the performance of Karl Mortar in Warsaw to be successful. They suggested developing a more dependable fuse. In early September, after firing approximately a dozen rounds, the vehicle, No.VI Ziu, was transported back to Germany.
On the Western Front, the rapid Allied advance was approaching Paris when Hitler decided to destroy the French capital. To carry out this plan, Thor was designated to travel westward and participate in Paris’ destruction. To support this mission, the 428th Army Battery was established. However, the vehicle intended for this purpose never reached Paris. Instead, it was redirected to Warsaw and arrived there on the 7th of September 1944. Two days later, another vehicle from the 638th Battery reached the front line. The sole vehicle from the 638th Battery returned to Germany in late September 1944 for extensive repairs.
Combat Operations in 1944 and 1945
On 28th September 1944, the 638th Battery received orders to relocate to Budapest. The 428th Battery followed much later, on 10th October 1944. Both units began their operations briefly but were evacuated by 19th October. By mid-November 1944, both batteries had been relocated back to Germany.
The 428th Battery, equipped with two vehicles, was assigned to the German Ardennes offensive planned for the end of 1944. These vehicles reached the frontline on the 29th of December 1944. One of the vehicles had to be withdrawn on 6th January due to damage sustained from an Allied aircraft bombing attack while en route to the front. Due to the scarcity of spare parts, this vehicle could only be repaired using components salvaged from vehicle No.I. Interestingly, during its repair, the Germans added 15 mm high chevrons to improve traction on snowy terrain. Following a brief test run, this vehicle was deemed operational and ready for service on 3rd February 1945.
In March 1945, the 428th Battery was relocated to the Remagen area, where it attempted to bolster German efforts to stem the Allied advance across the Remagen bridge. By 20th March 1945, the battery had fired approximately 14 rounds in support of this objective.
On the 22nd March 1945, the status of the Karl vehicles was as follows: Vehicle No.I and IV were stationed at the Jüterbog training center. Since September 1944, Vehicle No.I had been slated to receive a new diesel engine. Vehicles No.II and V were deployed on the Western Front. No.VI was en route to Jüterbog for necessary repairs, but these were not completed by the war’s end. No.VII was out of service due to a lack of spare parts. No.III had sustained extensive damage when a round detonated inside its barrel. Although attempts were made to repair it, these efforts were ultimately unsuccessful.
Fate
The fate of the 7 vehicles was as follows.
| Vehicle | Fate |
|---|---|
| No.I | Captured by the Soviets in April 1945 |
| No.II | Captured by the Allies in March or April 1945 |
| No.III | Blown up to prevent capture |
| No.IV | Captured by the Soviets in April 1945 |
| No.V | Captured by the Allies in March or April 1945 |
| No.VI | Captured by the Soviets |
| No.VII | Captured by the Allies |
Surviving Vehicles
Of the vehicles captured by the Allies, at least one was sent to Aberdeen Proving Ground. Unfortunately, at some point, it was scrapped. According to T.L. Jentz and H.L. Doyle (Panzer Tracts No. Bertha’s Big Brother Karl-Geraet), the Soviets captured No.VI Ziu, which is now exhibited at the Russian Kubinka Museum. Interestingly, it has the nickname “Adam” painted on it instead of Ziu. According to Janusz Ledwoch (Gerät 040/041 Karl Mörser Tank Power Vol LIII), while the mortar and its carriage are from the No.I vehicle, the chassis was taken from the No.VI. This is possible, as all seven vehicles used interchangeable parts.
Conclusion
The Karl was an intriguing attempt to develop a super-heavy mortar mounted on a self-propelled chassis to enhance its mobility. It is often criticized as a waste of resources and manpower, considering that only seven vehicles were produced. But is this criticism entirely justified?
Despite its size and weight, the Karl had decent mobility and could be brought into action relatively quickly. Its 60 cm mortar possessed tremendous firepower, capable of inflicting extensive damage on fortified targets. On nearly all occasions when employed, the Germans found their performance satisfying. The major issue with the Karl was its purpose: dealing with fortifications, which were generally rare. Essentially, it was a specialized weapons system with few opportunities to be used in its intended role.
While undoubtedly effective, there were not many targets that required the 60 cm mortar for destruction. In this regard, the time and resources spent on the Karl could be considered wasted. The Germans probably did not need more than a few vehicles, as they were rarely employed in groups larger than two or three. Additionally, the short range of the 60 cm mortar was a significant drawback, requiring the vehicle to be close to the front line. Despite this, it was not until the end of the war that a Karl vehicle was extensively damaged due to enemy action.
In conclusion, the Karl was an expensive and overly specialized weapons system that performed well when engaging targets it was specifically designed to handle. However, its limited application and the infrequency of suitable targets made it a questionable investment of resources.
Karl-Gerät 040 (60 cm) Specifications |
|
|---|---|
| Crew | 21 men (commander, 18 gunners, a driver, and an assistant driver) |
| Weight | 124 tonnes |
| Dimensions | Length 11.15 m, Width 3.16 m, Height 2.75 m |
| Engine | Maybach MB 503A gasoline engine 580 hp @ 1.850 rpm / MB 507C diesel engine same power |
| Speed | 10 km/h, 6 km/h (diesel engine) |
| Range | 42 km, 60 km (diesel engine) |
| Primary Armament | 60 cm Mortar |
| Elevation | 0° – 70° |
| Firing Elevation | 55° – 70° |
| Traverse | 4° to each side |
Sources
D. Doyle (2005). German military Vehicles, Krause Publications.
D. Nešić, (2008), Naoružanje Drugog Svetsko Rata-Nemačka, Beograd
P. Chamberlain and H. Doyle (1978) Encyclopedia of German Tanks of World War Two – Revised Edition, Arms and Armor press.
T.L. Jentz and H.L. Doyle (2001) Panzer Tracts No. Bertha’s Big Brother Karl-Geraet (60 cm and (54 cm)
Janusz Ledwoch (2007) Gerät 040 041 Karl Mörser Tank Power Vol LIII
J. Engelmann (1991) German Heavy Mortars, Schiffer Military History
G. Taube (1981) Die Schwersten Steilfeurer-Geschutze 1914-1945, Motorbuch Verlag
Walter J. Spielberger (1993) Sturmgeschütz and its Variants, Schiffer Publishing Ltd.
