Competitor from Gorkiy
In September of 1941, the Artillery Committee of the Main Artillery Directorate (GAU Artkom) initiated work on installation of more powerful armament into the T-60 tank. Management of design groups from Molotov GAZ and factory #92 "Novoye Sormovo" (called "OAO Nizhniy Novgorod Machinebuilding Factory today), one of the leading tank and artillery cannon factories at the time, was called to a meeting to discuss this issue. These two factories were built in the same city, about 10 km between gates. If the development was a success, this would significantly simplify cooperation.
When replacements of the TNSh are discussed, it is often mentioned that the gun was picky and jammed often. Of course, there were such cases, but they were often connected with improper use of the system. Some complaints were the result of factories taking certain liberties in producing ammunition. There was even a decree issued by the GKO (#627, September 4th, 1941) prohibiting factories from making changes to the gun or its ammunition without the approval of the People's Commissar of Armament. Another important factor is that the program to improve the T-60's armament began in September of 1941, and complaints about the TNSh started arriving only in October. Before that, the complaints were not about the gun.
The tank with the new engine began trials on May 19th. The tank was artificially loaded to 6800 kg, which was equal to the mass of the tank that the factory design bureau was working on. The result of the trials, which lasted until June 9th, showed that the maximum speed of the T-60 with the ZiS-16 was 40.5 kph, 1 kph higher than expected. The engine was not as loaded as the GAZ-202, was not as loud, and there was no difficulty in servicing it. The main problem was the cooling system, which was deemed inadequate (to be fair, the T-60 with the GAZ-202 engine also had cooling issues). Overall, the idea of installing the ZiS-5 and ZiS-16 in the T-60 was deemed successful. In order to full test out the design, five tanks with new engines were ordered.
At the same time, factory #37's design bureau was working on a deeper modernization of the small tank. The issue was first raised at a meeting of the People's Commissariat of Tank Production on May 14th. The proposal was made by factory #37 and passed on through Military Engineer 1st Class Afonin and consisted of installing a 45 mm gun in the T-60 and increasing its armour to 35 mm. By the time the topic was discussed, the vehicle in question, indexed T-45, was almost ready.
The military was opposed to the idea. The development was considered irrational, since a more powerful gun and thicker armour would increase the load on the engine and transmission. The project was given the green light thanks to the chief engineer of the T-50 tank, S.A. Ginzburg, who was serving as the deputy chief of the technical department of the People's Commissariat of Tank Production at the time. Since April of 1942, Ginzburg was pushing the idea of building a light assault gun on the T-60 chassis at factory #37, and he had common interests with the factory's management. Ginzburg was present at the meeting where the proposal was made, and definitely had an influence on the decision. The minutes contain the following note: "Test this tank over 200 km. Send the results to GABTU. Don't make any more of these tanks for now."