In contrast to the main battle tank, which mounts a cannon and is optimized for mobile strike operations, the assault tank is an armored vehicle fitted with a large-caliber howitzer, primarily tasked with supporting infantry engagements and breaching enemy defensive positions.

In the spring of 1942, under the direction of the People's Commissariat of the Tank Industry, Factory No. 8 and Factory No. 183 jointly submitted a proposal for an assault tank based on the T-34 chassis, mounting the U-11 howitzer in a newly designed turret. Designated U-22, the concept was evaluated but quickly found to be impractical. The limited dimensions of the T-34 chassis imposed severe constraints on turret size, preventing the crew from operating the weapon effectively, while the projected performance offered little improvement over the existing KV-II heavy tank. Development was therefore abandoned at an early stage, leaving the U-22 as nothing more than a paper project.

In 1943, after the U-11 howitzer underwent further improvements and was redesignated the D-11/12, the People's Commissariat of the Tank Industry renewed its interest in converting the T-34 into an assault tank. Designated "D," the project was assigned to Factory No. 183, and a preliminary design was completed by March 1943. Like its predecessor, the U-22, the design was based on the T-34 chassis and mounted the D-11/12 howitzer in an entirely new turret, one larger than that proposed for the U-22.

Ultimately, however, the "D" project met the same fate as the U-22, never progressing beyond the drawing board.