Work on a radically new tank often results in the creation of intermediate vehicles. This exact thing happened with Soviet medium tanks in WW2. Several attempts were made to replace the T-34 with modernized vehicles. The first attempt was called T-34M, later the T-43 took a shot at the reigning champion. The results were similar: neither tank replaced the T-34. The first Soviet new generation medium tank, the T-44, travelled a long way and changed a lot before it entered production.
From evolution to revolution
One of the reasons for the T-43's failure was the desire to reuse components from the T-34. This approach had its upsides, as it would take much less time to put it into mass production. On the other hand, this led to a long delay in the development of the first variant and ended up dragging the second to its death. The tank was heavier than the T-34, which already weighed more than 30 tons, and this would inevitably result in issues with the running gear. The increase in protection also lagged behind expectations. Requirements increased after the Battle of Kursk, and the new T-43 would have to weigh 35-36 tons. The driver's hatch also made a comeback, weakening the upper front hull armour. Further development of the T-43 was pointless.