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SU-7 203 \ 305-mm self-propelled artillery mount of special power

In addition to the super-heavy self-propelled guns SU-14 in the Soviet Union developed no less ambitious (but quite feasible) self-propelled gun projects with large-caliber guns. A few years earlier, as part of the terms of reference for the Special Purpose Triplex Artillery (TAON), a special group of designers assembled from Bolshevik and No. 185 factories began designing such self-propelled guns. The head of the team was appointed P.N.Syachintov. Consideration of the issue of preliminary design took place at GAU RKKA on October 1, 1933. “Triplex” provided for the installation of three different guns on a single chassis and carriage.

After exactly a month, NTU GAU formulated the specified requirements: “A 254 mm high power (BM) gun. The angle of vertical guidance is from 0 ° to + 42 °. The weight of a high-explosive bomb is 225 kg, the initial velocity of the bomb is 692 m / s, the firing range is 23500 m. The weight of the barrel with a bolt is 24000 kg. 305 mm howitzer high power (BM). The angle of vertical guidance is from 0 ° to + 60 °, the weight of a high-explosive bomb is 365 kg, the initial velocity of the bomb is 360 m / s, the firing range is 12500 m, and the initial velocity of the projectile is 600 m / s. The total weight of the gun is 14100 kg. 400 mm high power mortar. The angle of vertical guidance is from + 5 ° to + 70 °, the weight of a high-explosive bomb is 860 kg, the initial velocity of the bomb is 320 m / s, the firing range is 10500 m, and the initial velocity of the projectile is 600 m / s. Gun weight - 10,000 kg. "

Since one plant was not able to cope with the manufacture of all the components and assemblies of self-propelled guns, the design of the swinging part of the gun was transferred to the Bolshevik plant, and the chassis was to be manufactured at plant No. 185. Not having had time to begin the production of working drawings, design teams had to urgently finalize the project in view of the changing requirements. The GAU considered that the range of the 254-mm guns is insufficient and should be increased by at least a third. However, this would lead to the fact that the resource of the gun with increased power amounted to about 100 shots. It would be possible to use guns of caliber 210-220 mm, but such in 1933 did not yet exist.

Understanding the unreality of their requirements, the Main Department considered that the triplex can be replaced with a 203 \ 305 mm duplex. At the same time, the issue of reducing the mass of the gun was considered. At the next GAU conference, held in December 1934, the corresponding projects of the SU-7 self-propelled guns were presented on a chassis designed by Plant No. 185. The design of the gun was as follows:

• the swinging part was enlarged and executed as Schneider with a variable rollback
• the barrel structure as a whole repeated the barrel from a 203-mm howitzer B-4 with a free barrel
• the shutter was single, made by the type of shutter 152-mm guns B-30 or U-10
• the machine is made according to the type of machine 203-mm howitzer B-4.

At the same time, the project of the Bolshevik plant, developed under the direction of Magdisiev, had a fixed chassis and an overweight of 9 tons.

The project of plant No. 185 (supervisor Sjachintov) was equipped with a removable undercarriage and almost met the required 35 tons. However, the GAU rejected both options, citing the fact that the Magdisiev project would have poor agility, and the Syachintov project could not be embodied in metal because of the great difficulty in manufacturing individual elements of the chassis. Both design teams were given the recommendation to continue work on self-propelled guns with a fixed chassis.

A new project of the SU-7 heavy self-propelled gun was developed at Plant No. 185 under the direction of S. A. Ginzburg. According to the general layout, this self-propelled guns significantly stood out among the rest. In the front there was a motor-transmission compartment, and in the back there was a very spacious fighting compartment, where a 203 mm gun or 305 mm howitzer with 2-3 recoil brakes on the sides and two knurls under the barrel could be installed. The gun had a maximum elevation angle of up to 52 °, a howitzer - up to 70 °. The horizontal aiming angle was + \ - 42 °. Ammunition load ranged from 2 to 6 rounds. According to calculations, the rate of self-propelled guns was to be one shot in 80-100 seconds, with a coordinated calculation of 15 people, the electrical effect of winches and rammer. However, the mass of self-propelled guns increased to 102-106 tons at 75-80 according to the technical specifications, Since it was not possible to significantly reduce weight, the decree of October 1, 1936 GAU demanded to bring it to 100 tons.

Along with this, the ANII was entrusted with the development of rifled barrels and lighter armor-piercing shells. When using rifled shells, the caliber of the gun was prescribed to be considered exactly 203 and 305 mm, and when using belt guns - 8 and 12 inches, respectively. It would also allow the use of old naval shells that have remained in warehouses since the First World War and the Civil War. As a safety precaution, the Bolshevik factory was to develop a calibrated 203 \ 305-mm shell. This was done so that the 305-mm howitzer could replace the 203-mm gun, equalizing with it in firing range.

The production of working drawings and structural elements of the SU-7 began in the autumn of 1937. Billets of armored hulls were received from the Izhora plant, the modified GAM-34 engine, individual transmission units, etc. The chassis was assembled at factory number 185. It seems that the history of the SU-7 was developing quite successfully, but on October 2, 1937, the order of the head of the GAU N. Kirillov-Gubetskoy suddenly stopped to stop all work on self-propelled guns of high power, after which the half-finished self-propelled gun was dismantled for metal. The real reason for this step remained unclear.