Probably I'm trespassing again, but hope Mr. Holman will forgive me. The heaviest self-propelled guns in history have long deserved an entry here.
I'm talking about Karl, the 600mm (24-inch) mortar. Actually, seven guns with many names. Here is their story, brought to us by Mitch Williamson, the owner and author of the highly recommended War and Game blog.
The project began in 1936 and was known as Projekt 4 by August 1937. Then it became known as Gerät 040 (Device 040) by November 1940 then Gerät-Karl (Device Karl) by February 1941. The 54cm version was known as Gerät 041 by 1 July 1942 but by 22 July 1942 the name reversed to Karl-Gerät. An official list of cover names was released by OKH on 22 February 1943 with the 60cm Karl-Gerät named Gerät 040 and the 54cm version known as Gerät 041. If this is not already complicated the troops named each of the 6 guns as follows:
In a meeting on 9 March 1938 General Karl Becker ordered the go ahead for 6 production weapon systems along with a trial weapon (Versuchsgerät, mentioned elsewhere as "FENRIR").* Initially the Neubau Fahrzeug Nr. 1 (experimental heavy tank) was used to conduct driving trials in April 1938. In August 1938 a 1/10 remote controlled scale model was built for development of the suspension system. Parallel with this a test firing carriage was developed with the first test firing occurring from 23 to 25 June 1939. In October 1939 the design of a Munitionsschlepper (tracked ammo transporter) was authorized. This resulted in the use of the PzKpw IV chassis.
In October 1939 work also began on developing a means of rail transport for the weapon system. The first driving trials of a full size weapon system chassis began in May 1940. The weight of the actual weapon was simulated with special weights. In a meeting on 12 November 1940 it was authorized that a special trailer also be developed for road transport of the weapon system. The trailer was known as the Culemeyer-Strassenfahrzeug (road vehicle).
All of this information is to indicate that an actual complete prototype of the Gerät 040 was never built. Instead production of 6 systems began. The first complete Gerät 040 or Nr. I was demonstrated to Wa Prüf 4 on 2 July 1940 and the first rounds were fired [10 in total] by 5 November 1940. The last unit, Nr. VI, test fired 6 rounds on 28 August 1941. Firing dates for the others are as follows:
A Gerät 040 Nr. VII was scheduled to be completed by May 1942 and was reported as being used by the Waffenamt to create firing tables in September 1944. Not much else is known about this unit.
Here is some additional data on the units:
In February 1941 Waffenamt was given an order to increase the range of the weapon system. This resulted in the development of a 54cm gun to be designated as Gerät 041. Nrs. I, IV and V were modified to take the 54cm gun (actually they received a completely new 540mm/25 caliber barrel, thus falling out of the mortar category and becoming howitzers - LK). These were completed on 15 June, 7 July and 25 July 1944.
On 3 January 1941 Batterie 833 was established with KStN 501 at Bergen training ground. It was ordered to be combat ready by 15 February 1941. On 2 April 1941, a larger unit, Schwere Artillerie-Abteilung 833 (heavy artillery unit) was established with a Staff, a Staff battery and a 2. Batterie. At the same time the original battery 833 was renamed as 1.Batterie, Schwere Artillerie-Abteilung 833. On 14 May 1941 the 1st battery with two mortars [Nr. I and II] and 60 rounds of ammo was assigned to the 17.Armee and the 2nd battery with two mortars [Nr. III and IV] and 36 rounds of ammo was assigned to the 4.Armee.
Little is known about the 1st battery in the area of Lemberg where it was planning to engage the bunkers at Wielki Dzial. In several reports it is indicated that the it was not used and due to technical problems was non operational by 23 June 1941. The 2nd battery was used to engage the Brest-Litovsk fortress and by 24 June they fired almost all of the 36 rounds assigned.
By the end of June 1941 833 was sent home and they were rearmed by a towed 21cm Mörser 18 on 6 August 1941. They returned to the eastern front and left the Karl-Gerät's behind in Germany.
On 18 February 1942 they were ordered to supply personnel to create a battery of three Karl-Geräts. The mortars were transported to the 11.Armee, Heeresgruppe Süd to support the siege of Sevastopol. They were equipped with 72 heavy rounds and 50 light rounds of 60cm ammo. In a report dated 20 May 1942 the battery fired at Maxim Gorki and the Bastion forts. From 2 June to 6 June 1942 they fired 18 heavy rounds and on 7 June 54 heavy round and from 8 June to 13 June 50 light rounds were fired. By the 13th of June they were left without ammo. After receipt of an additional 29 heavy and 50 light rounds they fired 50 light on 30 June and 25 heavy rounds on 1 July 1942. On 19 July they were ordered back to Germany for restoration.
On 7 July 1942 833 was ordered to establish a new battery with two guns. This was established on 15 August 1942 and designated as Batterie 628(Karl). The unit was to go to the Leningrad area to support the siege. They arrived on 1 and 2 September however the attack was called off do to a Russian breakthrough. On 18 October 1942 OKH ordered Batterie 628 to proceed to Leipzig ASAP. This was rescinded and the batterie, with possible two additional Gerät 040 as reserve, was to support further attacks and it was planned that they were to fire 150 rounds. This was aborted because of Russian advances and by 4 December Batterie 628 was ordered back to Germany.
The next action for the weapon was to crush revolts in Warsaw and Budapest. After being inactive for over a year a single unit battery was ordered established on 13 August 1944 for immediate transport to Warsaw. The batterie was designated as Heeres-Artillerie-Batterie(bo) 638 and was equipped with a 60cm weapon [Nr. VI].
Loading a 600mm shell during the Warsaw uprising. August 1944 (Bundesarchiv)
The effect of Karl-Gerät fire.
The building destroyed by a shell is no other than Prudential, one of the first European skyscrapers.
On 26 August 1944 another batterie named Heeres-Artillerie-Batterie(bo) 428 was established and it was planned to send it to Paris. However on 6 September 1944 it was transported to Warsaw. On 9 September another Gerät 040 was also sent to Warsaw and added to unit 428.
On 25 September 1944 unit 638 was sent to Budapest without and weapons, instead a single gun [Nr. V] was being sent to the unit in Budapest. Unit 428 was also sent to Budapest by rail leaving on 10/11 October 1944. On 19 October both units were ordered to return to the Warsaw area
On 29 September 1944 here is the disposition of all guns:
Other equipment was a follows:
Both 428 and 638 were sent to fight in the west. Nr. II [60cm] and Nr. V [54cm] were captured by the Americans while still on their railcar transporters sometime between 21 March and 11 April 1945. On 22 March 1945 Nr. I was sent to the western front as a 54cm gun and Nr. II as a 60cm gun also went west on 11 March 1945. Nr. VI was returning to Germany because of engine damage. Nr. I was at Jüterbog as a 60cm gun as was Nr. IV as a 54cm gun. Nrs. III and VII were being rebuilt and would not be available for a long period.
On 11 April 1945 Batterie 638 was ordered disbanded and the personnel were ordered to Batterie 428 which was being refitted. This unit probably was only involved in local defense as infantry since Jüterbog was overrun by the Russians on 20 April 1945.
In 1945, Nr. II ("Eva") as well as Nr. V ("Loki") were captured by US forces in the period 21 March to 11 April 1945. Nr. VII, the test weapon, was captured by the US Army in Hillersleben and shipped to Aberdeen Proving Grounds but later scrapped. One 60cm mortar, captured by the Red Army, is on display at Kubinka Museum near Moscow, although marked as Nr. I ("Adam") while the Western sources claim it is Nr.VI ("Ziu"). Nr. IV ("Odin") was also captured by the Red Army. A Pz IV carrier and two full guns were captured and one set brought to UTPG after the war, but scrapped later!
And some alternative history for a dessert. A Photoshopped image, taken from the Tsushima website (RU), shows a Karl-Gerät abandoned by the Nazis near Sevastopol. The ship in the background is Krasny Kavkaz light cruiser of the Soviet Navy.
Source for most of this data is the excellent publication by Thomas Jentz published by Panzer Tracts
* All variants saw combat. His (Jentz) book also states that many of the seven produced (yes seven not six) had interchangeable barrels from 60 cm to 54 cm and back. They were more active than I thought with service in many battles, including against the Remagen bridge!