U-20: the 85-mm SPG on T-34 chassis

[Minsk94]

The first attempt to build a tank destroyer based on the T-34 chassis was as early as in the summer of 1940. Two chassis without turrets were sent to the Factory #8 in Kaliningrad. It was in the same factory, a year earlier, that the 85-mm AA gun 52-K was created. It was done by modernizing 76-mm AA gun M1938 designed by M.N.Loginov. The 52-K was also designed under the supervision of Loginov and was based on the concept by G.D.Dorokhin. After testing, 52-K was accepted into mass production and has received the official index 52-P-365.
Originally it was intended to create two versions of SPG with 52-K located in a rotating gun compartment with an open top. The project was progressing very slowly, and eventually was abandoned.
In the fall of 1941 the Factory #8 was evacuated to Sverdlovsk. In November 1941 the UZTM Design Bureau started to work on the similar tank destroyer system designated "Самоходная артиллерийская установка У-20" (SPG U-20). On January 3, 1942 the project was already introduced to the upper management of UZTM. The works on U-20 were supervised by the famous artillery systems' designer F.F.Petrov.

SPG U-20 presented the medium tank T-34 with an open-top turret and the gun crew of two. The front armor of the turret was to be 45 mm thick, and the sides 20 mm. Instead of the 52-K gun it was intended to install U-10 gun that was to be constructed by placing 85-mm 52-K barrel (without a muzzle brake) on the cradle of 122-mm M-30 howitzer. That would allow to have a more compact artillery system as a result. But even with redesign as such the barrel would still extend more than 850 mm in the front of the hull, and at those times it was considered to be a big minus of a design.

In April 1942 it was decided that the design did not meet the expectations, and by decision of the Artcom of GAU RKKA, the project was closed.



In the same time the alternative tank destroyer version was developed. This version, designated "U-20-II", was also based on T-34 chassis.
The concept of U-20-II represented a T-34 hull with an open roof turret for a 3-men gun crew also. But the turret's frontal armor was 75 mm thick, and the side armor was up to 40 mm. This protection was much better than U-20 turret. The height of U-20-II was less than of U-20 (2475 mm). The extension of the barrel beyond the hull was also less - only 200 mm. The turret of U-20-II was also extended in length which allowed an entire 52-K gun to fit inside. But the breach would end up so far back that it is really questionable how this gun could be loaded...

Just like U-20, the U-20-II project was canceled in April of 1942.