Prior to the issue of the State Defense Committee order there were several other anti-fortification vehicle projects, all of which were halted. Later in the war these projects were restarted. In December 1942 three different designs of "pillbox killer" vehicles were introduced by various engineer groups from the major Soviet artillery and tank factories. All of these designs used the ML-20 gun as a primary armament, with the KV-1S heavy tank chassis. After some discussion, the project of Josef Kotin was chosen for further mass production. This design successfully combined the ML-20 and KV-1S chassis with minimal expense.