In 1942 Krupp started development on a heavy SP gun-carrier for the 17cm Kanone or 21cm Mörser by using Tiger automotive components like engine、transmission、steel road wheels and tracks. Complete weight with 8 men crew was about 60tons, armor thickness was 30mm at the front and 16mm on the sides, a top speed of 45km/h on roads was possible. The partly assembled prototype was found in 1945 by allied troops in Haustenbeck near Paderborn