In total, six Karl-class guns were manufactured. These guns had the names Adam, Eva (1st Batt.), Thor, Odin (2nd Batt.), Loki, and Ziu. The self-propelled version of the 60 cm siege mortar was ordered in June 1937. General Karl Becker (general) of the Artillery was involved in the development, (explaining where the huge mortar gained its nickname). The driving trials were held at Unterlüss in May 1940. Delivery of the six production vehicles took place from November 1940 to August 1941. In February 1941, discussions commenced concerning increasing the range of the weapon, and in May 1942, 54 cm barrels (Gerät 041) were ordered for the six vehicles. At a conference with Hitler in March 1943 it was stated that the first 54 cm Gerät 041 would be delivered by June 1943, and the third, by mid-August. The 60 cm and 54 cm barrels appear to have been interchanged as required.