The model 1939 was nearing 45 tons in weight, with a long hull (6.75 m/22.14 ft), relatively narrow if not for the very large tracks. The generous mudguards above gave exceptional room for storage. However, as no transmission was able to cope with such mass, the designers found an expedient, giving both prototypes and the SMK an old but sturdy Caterpillar system, which proved tricky, even unreliable in operations. The driver sat in the middle and the radio operator/machine gunner sat on the left, the three other crew members being located in and below the turret.