 From 1954 to 1955 this type was made even heavier, creating the "surblindé" ("Uparmoured") version with a lower turret and a higher hull with a pointed glacis like the IS-3, bringing weight to about 64 tonnes and the line-of-sight thickness of the armour to 200 mm.As this caused serious mechanical reliability concerns despite a reinforced suspension, from 1956 to 1958 weight was reduced to 57.8 metric tonnes by building a cast lower hull, creating the "surbaissé" ("lowered") with a lighter but again taller turret, the "Tourelle D" (fourth type turret).As problems with the preferred Maybach engine persisted, despite limiting the desired output to 1,000 hp, from 1955 onwards a special design team, brought over from Germany, cooperated with the AMX factory to solve them.