The SU-152 and Related Vehicles

CHAPTER 1. Lessons of the Winter War

The story of the development of heavy SP guns in the Soviet Union began in September 1931. The primary goal was to increase the mobility of heavy artillery through mechanization. The SU-7 and SU-14 SP guns were developed during work on a “self-propelled corps-level triplex.” The SU-7 was designed to carry the 152 mm gun, the 203 mm howitzer, and the 305 mm mortar. The SU-14 was designed for the 107 mm gun, the 152 mm gun, and the 203 mm howitzer. Two prototypes were built and assigned the designations SU-14 and SU-14-1. Both systems were initially armed with the B-4 203 mm super-heavy howitzer model 1931, which was later replaced by the BR-2 152 mm heavy gun model 1935. There was talk of starting mass production of the SU-14. The “small triplex” project was canceled on August 7, 1938, after the political arrest of N. N. Magdesiyev (developer of the B-4 howitzer), followed by the arrest of P. I. Syachintov, who headed up the work on the SU-14.

The subject of super-heavy SP artillery came to the fore again in late 1939. On November 30, units of the Red Army crossed the border into Finland, and the conflict that the Finns refer to as the Winter War got underway. The Red Army units quickly encountered the layered defensive line known as the Mannerheim Line. The assault on the line failed. The attacking units, which included tank units, suffered heavy losses, and the offensive bogged down. The Finns managed to hold out until late February 1940. The Mannerheim Line featured a high concentration of defensive structures, some of which could only be put out of action by direct hits from corps-level artillery weapons or super-heavy artillery. The Finns used a large number of antitank artillery guns, which made it difficult to defeat the bunkers. This situation gave rise to an acute need for self-propelled large-caliber guns with armor sufficient to at least protect against small arms and shrapnel.

At that time, Leningrad was the center of heavy tank and heavy SP gun development. In April 1938, a competition got underway between two design bureaus—the Kirov Factory and Leningrad Experimental Machine Building Plant No. 185 (S. M. Kirov). Plant No. 185 had acquired a great deal of experience developing tanks and SP guns (including the SU-7 and SU-14 discussed previously), but it only manufactured a few dozen vehicles between 1933 and 1940. The Kirov Factory could not boast of a large number of development projects, but it had one very well known product—the T-28 medium tank. In 1933, the factory’s special design bureau, SKB-2, converted that crude vehicle into the Soviet Union’s main medium tank of the prewar period. So when the Defense Committee under the Council of People’s Commissars signed Resolution No. 198ss, “On a Tank Armament System for the Red Army,” on August 7, 1938, these were the two candidates for developing a breakthrough tank to replace the T-28 and T-35.

Plant No. 185 started work on the T-100 tank (often simply called “100” in correspondence), and SKB-2 began developing the SMK tank (named after Sergei Mironovich Kirov). Mockups of both tanks were displayed in October 1938. The prototype of the SMK tank had been built by May 1, 1939, and a T-100 prototype was ready by July 1 of the same year. By that time, the competition included a third project: SKB-2 had developed the KV breakthrough tank (named after Kliment Voroshilov) based on the SMK. The decision to manufacture the KV was made on February 27, 1939; a mockup was displayed in March, and a prototype had been built by September 1. In contrast to the twin-turreted SMK and T-100, the KV had a single turret and was smaller, enabling the thickness of the armor to be increased from 60 to 75 mm.

Proving-ground tests demonstrated that the KV was the most suitable model for use as a breakthrough tank. A decision had been made to produce a pilot batch of 15 tanks even before testing began. The fate of the SMK and the T-100 remained unsettled during the autumn of 1939, but both tanks were having problems with the AM-34 engine. However, the SMK was the preferred choice because the T-100’s coil suspension was unsatisfactory, and the tank also had poor visibility. The main complaints about the SMK concerned the engine and cooling system, and the T-100 exhibited the same shortcomings. The war with Finland became a unique testing ground for the new breakthrough tanks. They were also seen as a potential platform for the development of self-propelled assault guns.

In mid-December 1939, the design bureaus at the Kirov Factory and Plant No. 185 were tasked by the Military Council of the Northwest Front to manufacture engineer tanks armored to protect against small arms and shrapnel. Plant No. 185 immediately began two projects: work got underway on an SP gun based on the T-100 chassis, and it was decided to add additional armor to the SU-14. Thus, instead of becoming a super-heavy SP gun, the SU-14 was turned into an armored bunker buster. It was thought that up-armoring finished SP guns would be the quickest solution, but in reality work was finished only on March 20, a week after the war ended. Also, the project to base a bunker buster on the T-100 chassis changed a great deal before production began. The vehicle was given the B-13 130 mm naval gun instead of the BR-2 super-heavy gun by order of Plant No. 185’s director, N. V. Barykov. In addition, the project, which was given the designation T-100X (100X), had to be revised because the superstructure proved to be too complicated. The simplified version was designated the T-100Y (100Y; later we also encounter the SU-100Y). The heavy SP gun had its first reliability trial on March 14; like the SU-14, it came too late for the war with Finland.

The Kirov Factory took an entirely different approach. The KV prototype (serial number U-0) arrived from the front on January 1940. This tank had been the reference standard for the pilot batch. At the request of the Military Council of the Northwest Front, the first four tanks were equipped with 152 mm howitzers for use against bunkers. A larger turret was quickly developed for that purpose. A team of SKB-3 designers led by N. V. Kurin developed a plan to install the new turret within a very short period of time. The plan initially called for installation of the 152 mm howitzer model 1909/30; the system was assigned the designation L-21. In its final form, the assault version of the KV received the tank version of the 152 mm M-10 howitzer with a shortened barrel. This chassis was given the designation MT-1. On February 10, 1940, the modified U-0 underwent firing trials, and on the 17th the U-0 and U-1 tanks were sent to the front. The first “large-turret KVs” saw action on February 22, and by March 3 there were four tanks of that type at the front. They were unable to make a significant contribution to the breakthrough of the Mannerheim Line. Still, some received as many as 15 hits in battle without having their armor penetrated.