In the summer of 1942, the Armament Department of the German Land Forces signed an agreement with Krupp and Rheinmetall to create an ACS on the Panther tank chassis. Options for installing a 128-mm K 43 gun and a 150-mm sFH 43 howitzer were considered. The projects were designated Grille 12 and Grille 15. They had a rear location of the combat compartment and differed only in the type of artillery system. Later, a requirement was adopted to install a 150-mm gun with a barrel length of 63 calibers on the Grille 15. Such a gun had the ability to penetrate 200-mm armor with shells at a distance of 4000 meters. However, the work was delayed, and the Grille 15 project was never completed