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.
CHAPTER 2.
A New Chassis
During the spring and summer of 1940, work was underway at the Kirov Factory and Plant No. 185 to design heavy SP guns based on the T-100 and SMK tanks. No final decision had yet been reached about the future of these two tanks. Plant No. 185 was struggling with the T-100 and vehicles based on it. In January 1940, Marshal G. I. Kulik had requested that a turret be developed for the T-100 to mount the M-10 152 mm gun. That version was designated the T-100Z. In April, designers at Plant No. 185 developed a project for a coastal defense tank based on the T-100. It was assigned the factory designation 103. It differed from the similar T-100Y project in that it had the B-13 130 mm naval gun in a rotating turret. Similar projects were also underway at the Kirov Factory: correspondence indicates that there were projects for mounting the B-13 130 mm naval gun and even the B-1-P 180 mm naval gun on an SMK chassis. Unfortunately, information about these projects is unavailable.
On June 11, 1940, a document appeared with the title “Proposals for Refining the Tank Armament System,” which also made mention of the following SP assault guns:
1. The KV tank must have a 76 mm gun with a muzzle velocity of at least 800 meters per second in order to have the capability of piercing 70–80 mm of armor. The gun must have a rapid-fire capability and a sufficient supply of rounds.
The gun currently most suitable for the purpose is the 76 mm antiaircraft gun model 1931. The tank must have armor between 90 and 100 mm in thickness.
2. The KV-2 tank must have a 107 mm gun with a muzzle velocity of 730–750 meters per second in order to be capable of penetrating 100–110 mm of armor. The gun should be capable of rapid fire, possess excellent penetration capability, have a sufficient supply of rounds, and fire a time-fuzed shell in addition to an armor-piercing projectile.
The most suitable gun type at the present time is the 107 mm M-60.
3. Have self-propelled, armored heavy artillery with the task of destroying reinforced concrete bunkers. As armament for the self-propelled turretless vehicle, use 122 mm, 152 mm, and 180 mm guns.
a) The most realistic way of solving this problem is to manufacture and mount a 100–130 mm gun on a tank chassis and equip it with an armor-piercing projectile capable of penetrating 130–150 mm of armor.
b) As a matter of urgency, build a prototype for mounting the 152 mm gun model 1935 (BR-2) on the SMK tank chassis and equip it with an armor-piercing shell system capable of penetrating 150–160 mm of armor and a concrete wall 1.5 m thick.
The gun must be protected by 60–70 mm of armor, and the entire system must weigh no more than 65 tonnes.
c) Mount a 180 mm gun on a turretless vehicle (the SMK chassis) and modify the suspension as needed and reduce the armor thickness in order to decrease the weight.