The SU-152 and Related Vehicles - читать бесплатно онлайн полную версию книги автора Yuri Igorevich Pasholok (CHAPTER 9. Exposed to the Elements) #11

CHAPTER 9. Exposed to the Elements

The idea of using a KV tank chassis as the base for an open heavy artillery system was first expressed in the fall of 1942. Eng. Col. Afonin, chief of the GABTU’s Armor Directorate, received a letter from Factory No. 92’s director, A. S. Yelyan, on November 26:

Comrade P. F. Muravyev, our senior design engineer, spoke with you while he was in Moscow about developing a 400 mm self-propelled gun based on the KV tank. We have now developed the idea to the point that we can discuss it in more detail.

We have developed a conceptual design of the system, which we will send you after verifying some information on the KV tank, and the T-34, which is completely unknown to us, but about which we hereby request information. We are particularly interested in the following data:

1. The gross weight of the KV-1 tank produced in 1941 (before the war with Germany) and the weight of its turret with the basic load for the 76.2 mm gun and the gun itself.

2. The gross weight of the KV-1 tank manufactured in 1942 whose weight was increased as a result of an upgrade, and the weight of its turret with the basic load for the 76.2 mm gun and the gun itself.

3. The gross weight of the KV-1S tank produced in 1942 after its weight was reduced, and the weight of its turret with the basic load for the 76.2 mm gun and the gun itself. Whether the overall length and width, the area of track in contact with the ground, the engine power, the engine and driver location, and the strength of the suspension and hull components were modified in order to reduce the tank’s weight. Whether the suspension and hull could withstand a load from firing of 100 tonnes acting as shown in the attached diagram, and how the tank’s engine and running gear would perform on the road if the weight of our new system, 20 tonnes, is added to its total weight (less the turret, gun, and basic load).

4. We are also working to mount the system on the T-34 tank. Therefore, we also request that you inform us how all running gear components, the hull, and the engine will perform on the road and under the loads shown in the attached diagram, because Factory No. 112 was unable to give us complete answers to these questions, citing their lack of strength calculations for the T-34 tank.

5. We are most interested in the KV-1S tank for installation of our system. According to information in our possession, its gross weight is 37 tonnes. If the turret, the gun, and the gun’s basic load weigh 7 tonnes, the entire vehicle will weigh 50 tonnes, i.e., the weight of the KV-1 tank manufactured in 1941 (before the war with Germany). That means that if the KV-1S’s engine, track, and suspension durability are the same as those of the KV-1 manufactured in 1941, the new vehicle’s road performance will be quite satisfactory. If these assumptions about the new KV-1S tank are reasonable, we request that an order be sent to Factory No. 92 for a set of drawings of the KV-1S hull and suspension and that Factory No. 92 be informed of the rationale regarding opportunities and ways of obtaining this tank for purposes of mounting a prototype of the system.

Based on your analysis, please advise which tank we should to settle on and issue an order to have drawings of that tank’s hull sent to Factory No. 92; we have drawings of the T-34.^{1}

Unfortunately, we still do not know what 400 mm mortar was planned for mounting on a KV-1S or T-34 chassis. Nothing is known about the development of such systems by Factory No. 92. Yelyan received an answer to his letter on December 14:

Operation of KV tanks has shown that the running gear and engine of the 50-tonne tank are under a heavy load and frequently break down. This led to the development of the lighter KV-1S tank, which weighs 42.5 tonnes.

The power of the KV-1S engine, its location, and the strength of its suspension and hull components differ little from those of the KV-1 tank.

We cannot say whether the tank’s suspension would hold up under a 100-tonne load because we have no experience with use of the system under such loads.

Without knowing the design characteristics of the mortar, we can draw no conclusions about the feasibility of installing it in the tank.^{2}

The idea of an open SP gun based on the KV-1S surfaced again in the spring of 1943. Paragraph 12 of a report on the state of SP artillery manufacturing and developmental efforts prepared by the GAU’s Artillery Committee addressed a “203 mm self-propelled howitzer on a KV-1S tank chassis.” The report was dated April 28, 1943:

The April 15, 1942, resolution of a plenary session of the Artillery Committee proposed development of an engineering design for a BR-2 self-propelled gun on a chassis incorporating assemblies from the KV tank.

Experience gained in building vehicles between 1942 in 1943 has shown that a B-4 howitzer can be mounted on a KV-1S chassis in the form of a semi-enclosed vehicle.

By agreement with the 16th Department of the Artillery Committee, the Kirov Factory and Factory No. 172 are developing this project. Each factory is working independently.^{3}

^{400 mm SP mortar on the KV-1S tank chassis, November 1942 (TsAMO).}

^{V. G. Grabin — chief designer of Factory No. 92’s design bureau and, later, TsAKB. He developed numerous towed, tank, and self-propelled guns.}

There is almost no information about the Kirov Factory design. According to the correspondence, drawings of the rounds and traversing mechanisms of the B-4 and BR-2 guns were sent to SKB-2 on June 19, 1943. Work ceased at that point. No information about this project exists in SKB-2’s experimental work. Publications by some Russian authors mention similar efforts at the Ural Heavy Machinery Plant, but they found nothing like that among the Sverdlovsk projects. These projects may have involved mounting the BR-2 and U-3 in the SU-152, but these are SP assault guns, not open vehicles.

As far as Factory No. 172 is concerned, its design bureau developed the M-17 heavy SP assault gun with the M-40 203 mm howitzer, which clearly was not what the GAU’s Artillery Committee was asking for. As discussed above, instead of the M-17 the GAU’s Artillery Committee and the Technical Council of the People’s Commissariat of Arms required Factory No. 172 to develop a design for an open SP gun chassis armed with the B-4 203 mm heavy howitzer. Despite the fact that the task was issued in July 1943, there was no activity on that project in either August or September. In early September, the Central Artillery Design Bureau was added to the heavy SP gun program, and some of the designers who had proposed a similar SP gun less than a year previously were transferred to it.

It is worth noting that, in addition to the KV-1S chassis, the TsAKB was also considering other platforms for mounting the BR-2 and BR-4. A September 8, 1943, letter discussed transferring to the design bureau materials for SP gun projects based on the T-34 that Factory No. 221 had developed in early 1942. The BR-33P and BR-33G were then scrapped as not conforming to the specifications for bunker busters. That is absurd because the wording of the specifications changed radically a year and a half later:

The TsAKB of the People’s Commissariat of Arms has appealed to the GAU’s Artillery Committee with a request for materials in the Artillery Committee’s files on the 203 mm and 152 mm SP guns developed by Factory No. 221.

In early 1942, Factory No. 221 submitted projects for 152 mm and 203 mm self-propelled guns on chassis incorporating T-34 tank assemblies for a finding by the Artillery Committee.

The Artillery Committee approved these projects, but the situation at the time prevented them from being implemented.

In the belief that it is desirable and timely to begin developing new heavy self-propelled guns, and as one version of a plan prepared by Factory No. 221, which the Artillery Committee currently approves, I hereby request that the appropriate task for completion of this project be issued to TsAKB of the People’s Commissariat of Arms.^{4}

^{M22 203 mm self-propelled gun, October 1943 (TsAMO).}

On September 15, 1943, when the decision was made to continue work on tank, towed, and self-propelled artillery, the TsAKB was the only bureau working on SP guns mounting the B-4 and BR-2. According to documentation, the project was not a high priority. Nevertheless, on October 8 People’s Commissar of Arms Ustinov reported to Beria on the status of the Central Artillery Design Bureau’s new SP gun projects:

The Central Artillery Design Bureau (TsAKB) of the People’s Commissariat of Arms for lightly armored, semi-open vehicles for the BR-2 152 mm gun and the B-4 203 mm howitzer, as well as a closed assault vehicle for a 152 mm gun with the ballistics of the BR-2 and a 203 mm howitzer with the ballistics of the B-4.

For the TsAKB to manufacture prototypes of the vehicles, it needs to obtain from the People’s Commissariat of the Tank Industry two KV-1S or IS tanks without guns and turrets, one SU-152 chassis without its gun, and drawings, including general view drawings, of the KV-1S and IS tanks and the SU-152 vehicle.

I hereby request that the People’s Commissar of the Tank Industry (Comrade Malyshev) be instructed to act accordingly.^{5}

An unexpected competitor to the TsAKB project emerged just a few days later. On October 15, a letter forwarding the engineering design for the M22 SP gun was sent to the Technical Council of the People’s Commissariat of Arms, the GAU’s Artillery Committee, and the GABTU. Judging by the dates on the drawings, this SP gun had been developed in early October under the leadership of V. A. Ilyin, chief of Factory No. 172’s artillery design bureau. Despite the fact that this project was not recorded in the factory’s plans, the M22 was not his own initiative, as is evident from a memorandum:

Based on GAU Artillery Committee letter No. 829360s and People’s Commissariat of Arms letter No. 1888s, dated August 28, the Design Bureau of Factory No. 172 has developed and hereby submits the conceptual design for the M22 203 mm self-propelled howitzer.

The M22 system involves mounting the traversing mechanism of the B-4 203 mm howitzer on the KV-14 tank chassis.

This project entails little design change to the B-4 howitzer or the KV-14 tank chassis. The changes are as follows:

The recoil distance is taken to be 860 mm (the relative position of the rod and counter-rod recorded on short recoil) due to the possible lowering of the line-of-fire height and the need to stabilize the entire system during firing and while traveling.

The recoil resistance needed to be reduced from 88 tonnes to 45 in order to ensure stability during firing.

The design calls for adding a muzzle brake with an absorption coefficient of 48.9% to achieve that.

The design calls for removing metal from the muzzle and giving up the barrel’s normal safety margin in order to keep the center of gravity of the tipping parts on the trunnion axis.

The rest of the B-4 howitzer traversing mechanism remains unchanged.

The howitzer is mounted on a special raised area on the tank hull without inclusion in the mantlet, which made it possible to reduce the weight of the vehicle with its full complement of 26 rounds to 43 tonnes.

To protect the howitzer against bullets and shrapnel, it is equipped with a gun shield attached to the top carriage.

The projectiles are located on special racks above the engine compartment.

Loading is done manually by two or four men using a loading tray.

When loading, the tray is brought to the rack, and one man rolls a projectile into it.

This loading method is simple and enables a good rate of fire, considering the overall dimensions of the system.^{6}

^{Muzzle brake for the M22 203 mm SP gun (TsAMO).}

The delayed response by Factory No. 172’s design bureau to the requirement to develop a semi-open SP gun mounting the B-4 howitzer can only partially be attributed to installation on the chassis of the SU-152. Almost nothing remained from the original chassis; the initial KV-1S tank was actually wellsuited to modification for this purpose. To achieve the significant reduction in the height of the SP gun, only the tipping parts were taken from the B-4, and the howitzer itself was somewhat modified, of course.

Unfortunately, the situation at that point did not favor the M22. The design was submitted later than its competitor from the TsAKB. Even a week’s delay mattered at this stage. In addition, Factory No. 172’s design team had made changes to both the design of the howitzer and that of the SU-152 chassis. The addition of a massive muzzle brake to an SP gun that was mainly intended to fire from cover clearly worked against the M22. In addition, the muzzle brake would raise a great deal of dust during direct fire, which would give away the gun’s position and make it difficult for the crew to fire the weapon. The outcome was inevitable: The technical Council of the People’s Commissariat of Arms ordered further work on the M22 to cease.

In late November 1943, Factory No. 172’s design bureau tried for a second time to push through a heavy SP gun project. On the 27th, the design bureau sent materials on the M24 203 mm howitzer project led by A. Ya. Drozdov to the GAU’s Artillery Committee. It involved mounting a barrel with the ballistics of the B-4 203 mm howitzer on the ML-20 152 mm gun-howitzer’s carriage. It also proposed that consideration be given to mounting a barrel with the ballistics of the BR-5 280 mm mortar (designated the M25) on the same carriage. A spot was also found at the end of the memorandum for mention of a self-propelled version of the two systems:

In addition, the traversing mechanisms of both the M24 and the above-listed options for mounting a barrel would also be beneficial for mounting on a vehicle for the same reason.

To illustrate that, the attached materials include a sketch showing the traversing mechanism of the M24 system mounted on a KV-1S or KV-14 tank chassis.^{7}

The version of the M22 with an M24 gun was assigned the factory designation M26, and the version mounting the M25 was designated the M27. According to the memo, they planned on using the KV-1S or IS as the chassis. However, the only difference between the M26 and the M22 was that the M26 had a new gun system and no shield. In addition, the project envisaged placing the BR-2 152 mm gun on the same carriage. This was the M23 152 mm gun, which was under development at the same time.

On 15 December, the GAU’s Artillery Committee reviewed the M24 howitzer project. It was decided to proceed with that project and turn it into metal while at the same time rejecting the version with the barrel from the BR-5 280 mm mortar. The M26 and the M27 were not even mentioned. The TsAKB’s brainchild thus was finally left with no competitors.

^{M21 heavy 122 mm SP gun, 1:35 scale drawing.}

^{M21 122 mm heavy SP gun, 1:35 scale drawing.}

There was some backstage maneuvering going on with the transfer to TsAKB of KV-1S and SU-152 vehicles in repair status that Grabin had requested to serve as chassis for new systems. It became clear in 1943 that production of the KV-1S and SU-152 was coming to an end. The TsAKB chief therefore requested one IS tank and the drawings for it in addition to an order for two KV-1S and one SU-152. GABTU sent a report about that to Beria on October 11:

In accordance with letter No. NV-10/5070, dated October 6, 1943, from Comrade Ustinov, the People’s Commissar of Arms of the USSR, I hereby report the following:

1. Two type KV-1S tanks without armament and turret may be transferred from repair status to the Central Artillery Design Bureau of the People’s Commissariat of Arms, since new KV-1S tanks are no longer in production.

2. One SU-152 self-propelled gun in repair status may also be transferred.

3. General-view drawings of the hulls of both the KV-1S tank and the SU-152 may also be transferred by the People’s Commissariat of the Tank Industry, for which transfer People’s Commissar Comrade Malyshev has given his consent.

The People’s Commissariat of the Tank Industry may only transfer an IS and the drawings for it after testing of the tank is complete and the drawings are brought up to date, because only prototypes of IS tanks are currently being manufactured. They will not complete testing and go into production until November of this year.^{8}

^{M24 203 mm howitzer considered as armament for the M22 SP gun (KBM).}

^{S-51 203 mm SP gun in travel position (TsAMO).}

Two KV-1S tanks and one SU-152 were sent to TsAKB in November. Because the bureau had begun working on new systems, in a letter dated November 10, Grabin tried to get a KV-85 in place of one KV-1S. The request was granted: TsAKB tested an S-34 100 mm gun on the KV-85. The design bureau did not make use of the SU-152 because subsequent projects involved the ISU-152.

The situation with development of the semi-open SP guns equipped with the B-4 howitzer was also quite interesting. The fact is that the design bureau was working on systems without having clear specifications for them. With only a vague assignment in hand, TsAKB initially considered several options for the SP gun chassis. The situation was unchanged in October; TsAKB decided to undertake the project without approved specifications. The GAU’s Artillery Committee finally drew up an operational requirement “for 152 mm and 203 mm auxiliary-propelled guns for the Artillery Reserve of the High Command (ARGK)” on November 16. It was signed by GAU chief Col. Gen. Yakovlev on November 18:

I. Definition and role.

1. The auxiliary-propelled ARGK guns consist of an open system with the traversing mechanism of a 152 mm gun model 1935 (203 mm howitzer model 1931) mounted on a special chassis incorporating assemblies from KV or IS tanks and having light armor protection only in the front.

2. The ARGK auxiliary-propelled guns are heavy mobile artillery guns attached to large units on the main axis of advance.

3. The guns are intended to accomplish the following fire missions: destruction of enemy concrete fortifications, including by direct fire at ranges of 1500–2000 meters, and the destruction and suppression of enemy artillery.

II. Main specifications

A. The cannon unit.

1. The following basic specifications apply to the cannon unit of the ARGK auxiliary-propelled guns:

- Vertical arc of fire from -3° to +65°

- horizontal arc of fire 60°

- traverse rate: same as for the BR-2 and B4 systems

Rate of fire:

- for the 152 mm gun 2–3 rounds per minute

- For the 203 mm: 1–2 rounds per minute

Basic load transported with the gun: 10–12 rounds

Gun crew (including driver-mechanic): 8

Time for transition to and from travel and firing positions: not more than 2 minutes

2. Weight of gun in firing position: 45–48 tonnes

3. The gun’s front armor protection must consist of a gun shield with lateral extensions about 35 mm thick (for protection against shrapnel).

4. For convenience of crew operation in the travel position, the area of the platform may be extended by means of folding decks that are stored for travel.

5. To support delivery of fire throughout a 60° arc, vehicles may be equipped with side-mounted (anchor type) trails.

6. For long marches, the guns may have provision for a special travel position accomplished either by rotating the traversing mechanism by 180° or by retracting the barrel.

7. For loading the guns, a special device must be developed that is actuated either by means of a motor or manually (requiring no more than 4 people to operate).

The guns may have a set loading angle in accordance with the design of the BR-2 and B-4.

8. The guns must incorporate the sights normally used for the B-4 and BR-2 that support both direct fire and fire from maximum range.

9. Each gun must be equipped for both radio and telephone communications.

B. The chassis.

10. To achieve the specified weight, the chassis must be made of high-hardness steel armor plates 35 mm thick.

11. Special braces may be used inside the hull of the vehicle.

12. The chassis may be lengthened as required to accommodate an additional road wheel.

13. It would be desirable for the gun to retain the speed of movement and mobility of the IS-152 vehicle.

14. Fuel endurance: 100–120 km

III. General requirements.

1. The gun crew must be provided with seats for long marches.

2. The chassis must have areas for storage of a SPT&A for the gun and vehicle, the telephonic communications equipment, a first-aid kit, dry rations, and the crew’s personal gear.

3. The bow and the stern must have tow hitches like those on the IS tank.

IV. Additional specifications.

1. For transporting ammunition in excess of that stored on the vehicle and intended for carrying out a specific fire mission, develop a tracked armored trailer capable of carrying 50 rounds for the B-4 or 100 rounds for the BR-2 that can be towed behind the vehicle.^{9}

Ironically, the specifications for vehicle type and weight differed little from those for the heavy SU-14 SP gun developed 10 years previously.

Manufacture of the SP gun, dubbed the S-51, began in January 1944. In theory, mounting PB-4 on the KV-1S chassis required extending the hull and adding an additional pair of road wheels. Also, talk about a special chassis during wartime was tantamount to putting a project on the back burner. Therefore, TsAKB decided not to modify the running gear. The only changes made to the KV-1S in repair status had to do with mounting the new gun on it.

The tipping parts of the B-4 203 mm howitzer were adopted without change. The gun was moved far forward; its base partially overhung the driver’s compartment. The howitzer barrel was retracted in the travel position. The gun was mounted on a special frame that partially obscured the view from the driver-mechanic’s vision block. The system did not have a gun shield at first. Later, a 7 mm thick gun shield was installed to protect the crew against shrapnel. The shield consisted of two parts that folded forward to facilitate movement of the B-4 barrel from the travel position to the firing position. When that was done, the shield rested on special supports on the vehicle.

A platform to hold some crew members when the gun was in firing position was built on shelves over the S-51’s tracks. The platform’s internal spaces served as containers for the SPT&A, and the platform was given a railing to prevent accidents. The main ammunition was stored in regular wooden boxes that were attached to rails and lay on the floor of the platform while the gun was in travel position. Fold-out ladders were added to the SP gun’s stern to facilitate getting on and off the vehicle. Folding guide rails on which a loading tray was placed were located between the ladders. The guide rails were primarily needed for loading the gun from the ground. The S-51’s basic load consisted of just 12 rounds. When firing from cover, therefore, the basic calculation was based on the ammunition carried. It should be noted that when the S-51 was in firing position, part of its 10-man crew was located on the vehicle and the rest on the ground.

^{Rear view of S-51 203 mm SP gun in travel position (TsAMO).}

^{S-51 203 mm SP gun in fighting position (TsAMO).}

^{Right side view of S-51 203 mm SP gun in fighting position (TsAMO).}

^{S-51 SP gun at maximum elevation (TsAMO).}

The heavy, open-type SP gun program entered its active phase in early February. The S-51 continued to be a low priority and therefore is not included on the list of high-priority programs mentioned above. The SP gun was first mentioned in a letter Ustinov wrote to Yakovlev on February 15, 1944, concerning the finished vehicle:

This is to inform you that the TsAKB of the People’s Commissariat of Arms has manufactured the B-4 203 mm howitzer on a KV-tank chassis (the S-51 system). The S-51 system underwent factory firing tests at Factory No. 88’s test range (at low elevation angles) and at the Sofrinsky Artillery Range of the People’s Commissariat of Munitions (at high elevation angles). During the factory tests, 49 rounds were fired. The S-51 system past both the factory firing tests and the road test done at the same time. During the tests, a rate of fire 30% higher than that obtained on the V-4 system on this normal carriage was measured.

Before the S-51 system is handed over for proving-ground tests, TsAKB is modifying the system in accordance with instructions received from the Artillery Committee Chairman Lieut. Gen. of Artillery V. I. Khokhlov (it is adding an armored shield for protection against small arms fire).

I hereby request your guidance on conducting proving-ground tests of the S-51. It would be advisable to carry out these tests at the Sofrinsky Artillery Range of the People’s Commissariat of Munitions because the Gorokhovets Artillery Proving Ground lacks the hoisting equipment needed to disassemble the system before and after testing.

This disassembly can be done in TsAKB shops.

Please provide information about the test program and the procedure for performing such tests as you deem necessary.

I further report that the S-51 development project of TsAKB of the People’s Commissariat of Arms also examined installation of the BR-2 152 mm gun on the same chassis.

Under our agreement with you, we anticipate receiving the BR-2 system in TsAKB in order to manufacture the prototype vehicle for this gun. TsAKB has a KV tank for building the vehicle.^{10}

The GAU’s Artillery Committee approved the test program for the S-51 on March 2. The SP gun had arrived at the Gorokhovets Artillery Proving Ground prior to that—on February 26. The technical documentation came two days later. The problem with the lack of hoisting equipment at the proving ground was solved by breaking down and measuring the howitzer at Factory No. 112. However, the system could not be disassembled as completely as required. Before the tests were performed, the S-51 traveled a distance of 150 kilometers, 120 kilometers of it traveling from the proving ground to Factory No. 112 and back.

Testing of the SP gun began on March 16, 1943. Because the proving ground lacked high-explosive shells for the B-4, the test for firing accuracy was performed using concrete-piercing projectiles, thus shortening the proving-ground tests. On the 16th, 18 rounds were fired. During the entire course of the firing test, which lasted until March 24, 209 rounds were fired, 135 of them supercharged.

During firing at an angle of 30°, it was found that the S-51 moved backwards 1000–1300 mm, and it had a counterrecoil of 200 mm. When fired, the SP gun’s bow lifted 250 to 450 mm, and its stern lowered by 200–300 mm. At the same time, it was observed that the right side jumped by 100 mm more than the left. When fired at an angle of 45°, the vehicle moved backwards 750–1000 mm; it had a counterrecoil of 330 mm; its bow lifted 100–180 mm; and its stern lowered by 120–140 mm. Firing at an angle of 57° revealed a backward movement of 400–750 mm, a counterrecoil of 300 mm, an upward movement at the bow by 60–150 mm, and a downward movement at the stern of 50–100 mm. Thus, the S-51’s stability was considered unsatisfactory. The sight was also highly unstable.

Firing for durability (with 100 supercharged rounds), no damage was found on inspection. The rate-of-fire tests with a seven-man crew yielded an average figure of one round every 1.5 minutes.

^{Front view of S-51 SP gun at maximum elevation (TsAMO).}

The road tests took place between March 25 and April 4. The SP gun was tested under different road conditions; the snow depth reached 200 mm. Overall, the S-51 travel 524 kilometers, 16 of them on cobblestones and 40 off road. Most of the on-road tests took place on asphalt highway, as required by the trips to Factory No. 112. A maximum speed of 32 km/h was reached in the on-road tests, and 22 km/h off the road. No special tests were carried out because of various running-gear failures. At 240 kilometers, the right-side steering clutch and brake band went out, and the right steering clutch broke down again at 360 kilometers. Problems occurred with the tracks several times; bolts on the track roller cap broke. However, there were no problems with the engine or torsion bars, again confirming the durability of the running gear after the firing test program.

The tests concluded on April 6, and the proving-ground commission issued the following finding on the 9th:

1. The S-51 self-propelled howitzer successfully passed most tests because:

a) The operation and durability of the gun’s assemblies and mechanisms are satisfactory.

b) The durability of the gun mounting parts is satisfactory.

c) The operation and durability of the vehicle assemblies and mechanisms are satisfactory, except for the transmission group, which had a number of defects during testing caused by its overall poor technical condition prior to the tests and wear to parts.

2. Shortcomings of the S-51 self-propelled howitzer during firing are as follows:

a) A large movement backwards and instability of aim, especially at low elevation angles, due to the vehicle’s instability during firing.

b) A large lateral spread of rounds caused by sideways movement of the gun during firing.

These flaws can be eliminated by placing trails on the vehicle’s rear as was done on the SU-14 203 mm self-propelled gun designed and manufactured by the Kirov Factory, which underwent proving-ground tests in 1936.

Considering that the howitzer will primarily be fired at high angles of elevation during which backward movement and instability of aim are less significant, the placement of wooden beams constructed from locally improvised materials can be recommended to eliminate the vehicle’s backward movement on the rare occasions when the gun is fired at low angles of elevation.

3. The Gorokhovets Artillery Proving Ground believes that the S-51 203 mm self-propelled howitzer is more maneuverable and exhibits better firepower and lethality than the B-4 203 mm howitzer, and it can be recommended for adoption by the Red Army when the flaws identified during testing and noted in this report are corrected.^{11}

Based on the test results, Grabin wrote Beria to express his thoughts about putting the S-51 into production. The TsAKB’s chief felt that a total of 20–30 SP guns of that type should be manufactured. The Self-Propelled Artillery Office had a negative reaction to that idea. They felt that it did not make sense to use the KV-1S chassis to manufacture a heavy SP gun with a light gun shield. In addition, the S-51’s combat weight was 50 tonnes, and the tankers still remembered the way things were in 1942 when KV-1 tanks weighing that much were dropping their engines and transmissions. A decision was made to conduct additional tests on the SP gun, but they did not take place because the chassis required major overhaul after the road trips that spring.

^{Converting from travel position to fighting position (TsAMO).}

^{Rear view of S-51 SP gun. The fold-out ladders and guide rails for the loading tray are clearly visible (TsAMO).}

^{Firing trials. Part of the S-51 crew was located on the ground during firing (TsAMO).}

The S-51 program temporarily ground to a halt. GAU Artillery Committee chairman Lieut. Gen. Khokhlov attempted to get things moving again by sending Yakovlev a letter on July 22 expressing his thoughts about how the SP gun would be used in battle:

Because our troops will soon be crossing the border between the Soviet Union and Eastern Prussia, the Red Army’s artillery will acquire the mission of engaging the enemy’s permanent fortifications.

According to information from the Intelligence Directorate of the Red Army’s General Staff, the concrete in the fortifications in that region is between 1.4 and 2 meters in thickness.

The most suitable system for use against concrete of that thickness is the B-4 203 mm howitzer, which is capable of penetrating modern concrete of the following thicknesses:

At a range of 1000 m: 1.4 m;

At a range of 2000 m: 1.3 m;

At a range of 3000 m: 1.2 m.

Experience from 1939 through 1944 has demonstrated that this howitzer is most effective against concrete bunkers when fired from short range.

The TsAKB of the People’s Commissariat of Arms has developed and manufactured a prototype S-51 203 mm auxiliary-powered howitzer with the B-4’s traversing mechanism mounted on a KV tank chassis.

The prototype has been range tested with satisfactory results, except for stability during firing: a 1.5-m backward movement by the howitzer, and a 450 mm upward hop at the bow.

I believe that this system, which has greater mobility and fire maneuverability than the B-4 howitzer, can be successfully employed against concrete bunkers using direct fire.

The backwards movement of the howitzer can be eliminated by placing wooden blocks under the tracks.

I propose ordering a batch (several dozens) of these auxiliary-powered howitzers to be manufactured in August of this year. A production run of that size would be entirely realistic.^{12}

The letter forwarded a draft State Defense Committee decree “on the manufacture of a batch of B4-S51 auxiliary-powered 203 mm howitzers” that would clear the way for production of the S-51 in the event of a positive decision. The name of the person meant to sign the decree was not indicated, but Stalin usually put his own signature on decisions of that type.

1. Accept the B4-S51 203 mm auxiliary-powered howitzer developed by the Central Artillery Design Bureau of the People’s Commissariat of Arms with the traversing mechanism of the B-4 203 mm field howitzer model 1931 mounted on a KV-1S tank chassis for service with the Red Army.

2. The People’s Commissariat of the Tank Industry (Comrade Malyshev) and the Main Tank Repair Directorate of the Red Army (Comrade Sosenkov) shall deliver 50 reconditioned KV-1S tanks minus turrets and with running gear, engines (with no more than 10% of their operating hours used), transmissions, and complete field SPT&A kits in good working order to the People’s Commissariat of Arms by the following deadlines:

By August 10: 25

By August 25: 25

3. The People’s Commissariat of Arms (Comrade Ustinov) shall, by August 10 of this year, manufacture adapters and mounting parts using drawings produced by TsAKB and organize production engineering for the B4-S51 203 mm howitzers by the following deadlines:

By August 20: 20 auxiliary-powered howitzers

By August 30: 30 auxiliary-powered howitzers

4. During production, eliminate flaws with the 203 mm howitzer installation identified during proving-ground tests by requiring TsAKB (Comrade Grabin) to make the necessary changes to the drawings and submit them to the Red Army’s GAU for approval by August 1 of this year.^{13}

However, the decree was never signed. The repair plants were unable to provide the required number of repaired KV-1S chassis. Furthermore, chassis of that type were being used to manufacture recovery vehicles, which were urgently needed by armor units. In addition, the management of the Self-Propelled Artillery Office had a large number of questions about the S-51, as did Malyshev. Malyshev (People’s Commissar of the Tank Industry), Ustinov (People’s Commissar of Arms), Fedorenko (Main Armor Directorate), and Yakovlev (Main Artillery Directorate) came together for a meeting in late July 1944. Malyshev and Fedorenko were strongly opposed to manufacturing the S-51. Their argument was that the SP gun was obviously overloaded and could not sustain long-term use.

^{S-51 SP gun, 1:35 scale drawing.}

^{The BR-17 210 mm gun or the BR-18 305 mm howitzer mounted on a T-34 tandem tank chassis. This SP gun was considered an alternative to the S-51 and S-59 (TsAMO).}

Meanwhile, TsAKB continued working on heavy SP guns. In the summer of 1944, the design bureau built the S-59—an SP gun armed with the BR-2 152 mm heavy gun. To make it, TsAKB used a repaired KV-1S with hull serial number 30164 and engine number 309512 that had been provided by Repair Plant No. 1 on October 29, 1943. Few modifications were made because the same components were used for both the BR-2 and the B-4. According to the documentation, the S-59 was accepted for proving-ground tests in late August 1944.

However, the tests performed on the S-59 were largely academic because the KV-1S chassis had been rejected. The logical solution, which was settled on in late June 1944, was to replace the KV-1 chassis with an IS. Also, on July 29 the Leningrad branch of TsAKB proposed mounting the BR-17 210 mm gun or the BR-18 305 mm howitzer on a T-34 tandem tank chassis. This project was developed as an alternative solution. According to documentation, People’s Commissar of Arms Ustinov proposed drawing up an operational requirement for that vehicle, but it did not advance beyond the conceptual design stage.

On August 14, the chairman of the GAU’s Artillery Committee approved an operational requirement “for a 203 mm auxiliary-powered howitzer and a 152 mm auxiliary-powered gun based on the IS heavy tank.” The chassis replacement was not the only modification made to the future SP gun’s design. It was proposed that the vehicle be equipped with a turret-mounted DShK machine gun (with 1000 rounds of ammunition) for self-defense, and that it also have two DP machine guns (with 2520 rounds), four PPSh submachine guns (with 4000 rounds), and 25 F-1 hand grenades. The crew size was increased to 10, and the basic load from 12 to 15 rounds for the B-4, or 25 rounds for the BR-2.

On September 22, GAU chief Marshal of Artillery Yakovlev wrote a memorandum for Beria. In the memo, he suggested that consideration be given to producing a modified version of the SP gun that would thereafter be based on the IS tank chassis. The report also clarifies some details regarding the revised project:

In my letter No. 623605ss of July 27 to you I reported on the issue of manufacturing a batch of 203 mm self-propelled howitzers developed by the TsAKB of the People’s Commissariat of Arms (Comrade Grabin).

As your response to my report instructed, I have discussed the matter in a joint meeting with the People’s Commissariat of Arms, the People’s Commissariat of the Tank Industry, and the Main Armor Directorate.

We decided that it would not make sense to mount a 203 mm howitzer on the KV tank chassis, given that there are insufficient numbers available and that doing so would overload it. We would be better advised to mount this howitzer on the IS tank chassis, which is currently in production.

Based on that decision, GAU has issued the People’s Commissariat of Arms and the People’s Commissariat of the Tank Industry an operational requirement for a 203 mm auxiliary-powered howitzer on an IS tank chassis, and the People’s Commissariats have issued appropriate orders to TsAKB and Factory No. 100 concerning project development.

The Main Armor Directorate has no requirement for this type of weapon for the armored forces and has expressed no interest in developing a 203 mm auxiliary-powered howitzer. On the contrary, it believes that it would be inadvisable to use an armored chassis for this purpose.

The People’s Commissariat of the Tank Industry is of the same opinion.

That opinion is hindering development of this weapon despite the formal order from the People’s Commissariat of the Tank Industry to Factory No. 100 to undertake the project.

The GAU fully agrees that armor as strong as that on the IS tank is unnecessary for an auxiliary-powered gun and, in proposing that the IS be used, is thinking of the opportunity it offers to rapidly acquire a weapon of this type based on a system currently in mass production.

GAU believes that there is an urgent need for 203 mm auxiliary-powered howitzers at this stage of Red Army combat operations.^{14}

^{S-59 SP gun, 1:35 scale drawing.}

As in July, the report forwarded a draft State Defense Committee decree, this time for the “manufacture of 203 mm auxiliary-powered howitzers on the IS tank chassis.” This time the artillerymen’s appetite was more modest:

1. The People’s Commissariat of Arms (Comrade Ustinov and Comrade Kotin) and the People’s Commissariat of the Tank Industry (Comrade Malyshev) shall by October 15, 1944, prepare engineering drawings for a 203 mm auxiliary-powered howitzer based on the IS tank in accordance with the GAU’s operational requirement.

2. The People’s Commissariat of Arms (Comrade Ustinov and Comrade Grabin) shall send the number of designers required to coordinate all issues concerning mounting of the howitzer and developing engineering drawings to Factory No. 100 of the People’s Commissariat of the Tank Industry, where all of the work will be completed.

The GAU (Comrade Yakovlev) shall, upon completion of the engineering drawings, send a representative to Factory No. 100 to approve the drawings on site.

3. The People’s Commissariat of the Tank Industry (Comrade Mlyshev, Comrade Zaltsman, and Comrade Kotin) shall, upon securing IS tanks, manufacture a batch of 20 203-mm systems on IS tank chassis by the following deadlines:

During October: 5

During November: 15.^{15}

This second attempt at crossing the river turned out to be no more successful than the previous one. It should be noted that TsAKB was extremely cool to the idea of developing a system like the S-51 on an IS chassis. TsAKB’s deputy chief designer, K. K. Renne, wrote a letter to Khokhlov and Satel expressing the opinion that it would be inadvisable to take on another development project before the decrees are issued. In other words, TsAKB was holding firm to the idea of an SP gun using the KV-1S chassis. The People’s Commissariat of the Tank Industry and the Main Armor Directorate were also cool to the SP gun concept, but for a different reason.

It would be inadvisable to mount the B-4 203 mm howitzer on the KV-1S tank chassis for the following reasons:

1. The system would weigh about 50 tonnes, 7 tonnes more than the KV-1S, which would cause the vehicle assemblies to operate unreliably.

2. It would not make sense to manufacture an open artillery vehicle based on a tank with strong armor protection.

3. The KV-1S tanks have been dropped from production, and they would be difficult to repair due to the lack of spare parts.

The GAU’s Artillery Committee has developed an operational requirement for designing a 203 mm howitzer vehicle based on the IS tank.

In its letter No. 556976s of July 30, 1944, GABTU’s Self-Propelled Artillery Office wrote the GAU’s Artillery Committee concerning the inadvisability of using the IS tank with strong armor for an open 203 mm howitzer system.

The GABTU’s Self-Propelled Artillery Office has recommended designing a special chassis using assemblies from a heavy tank and a tractor.^{16}

^{A B-4 203 mm heavy howitzer’s crew conducts direct fire on the enemy, Berlin, April 1945. This photo might have featured the S-51 had it not been for the controversy surrounding the heavy SP guns (RGAKFD).}

The situation finally reached an impasse in November. On the one hand, the TsAKB had not warmed to the idea of reworking the S-51 project. On the other, both the People’s Commissariat of the Tank Industry and the Self-Propelled Artillery Office of the Red Army’s Main Armor Directorate were firmly opposed to both SP gun versions. In commenting on the draft State Defense Committee decree, Malyshev suggested designing a new SP gun. Under wartime conditions that essentially killed the project.

The story had come to an appropriate end. The controversy meant that the S-51 and S-59 went no further than the prototype stage, and the SP howitzer that the artillerymen needed so badly was never fielded. As they did in the winter of 1939–1940, the artillerymen “took down” enemy fortifications with heavy guns and mortars that were exposed to direct fire.

MAIN COMBAT AND TECHNICAL CHARACTERISTICS OF SP GUNS BASED ON THE KV TANK

MAIN COMBAT AND TECHNICAL CHARACTERISTICS OF SP GUNS BASED ON THE KV-1S TANK