The most important innovation was the standardized four-sided tower of increased size, protected by 9 mm (0.35 in) of armor. Elevation for the machine gun was raised to -10 to +37 degrees. A water tank was mounted just under the roof, to cool down the machine gun. Later, after field experiences, serial machines were fitted with a return roller on both sides and a modernized turret traverse system, although still carried out using a flywheel with reduction – five turns made for a complete revolution. Maximum protection was now 12 mm (0.47 in) on the chassis nose glacis. The engine was upgraded to the Meadows ESTE, giving 88 hp. Production lasted from 1934 to 1935 but was discontinued and eventually stopped because of several issues. The attempt to simplify the design had reduced its driving performance. A higher hull and heavier turret meant the gravity center was higher up, making the tank much more unstable. In addition, the Vickers machine gun was already clearly inadequate. Unfortunately, at that time, the Besa 13 mm (0.51 in) was not ready yet, and would have probably increased the stability problem. Only 34 rolled off the line.