A proposal to install a more powerful 350 hp Renault engine only partly compensated for a drop in mobility due to the weight increase. It transpired on 13 April 1939 that the intended ARL3 turret, bringing the proposed tank's height to 325 cm, could not be fitted without making the design too wide for rail transport, and further that the weight, now projected at 37.5 metric tonnes, would exceed pontoon limits.
The development of a new tank faced difficulties in its design due to the need for a more powerful engine, but this was not enough to overcome the increased weight and the size limitations imposed by the intended turret and the weight limits of pontoons.