The T-40 was an improvement over the T-37 and T-38 in several respects. The coil-spring suspension of the T-38 was replaced by a modern torsion-bar suspension with four pairs of road wheels. The boat-shaped hull was entirely welded, in contrast to the riveted hulls of the T-37 and T-38. The welded, conical turret shape improved protection, although the armour was still very thin. Armament was a 12.7mm DShK heavy machine gun, a much more potent weapon than the 7.62mm DT machine gun mounted on the T-38.