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In autumn 1944, production of a new mid — weight self-propelled gun, designated SU-100, with the D-10S 100mm Main Gun was started at  UZTM. Within its class, the vehicle was manoeuvrable and well protected, with 75mm thick sloped frontal armour. (For comparison: the SU-152 Heavy Assault Gun was also protected by 75mm thick frontal armour). In spite of this, there were some shortcomings common for vehicles with crew compartments located at the front. The long gun barrel increased the overall length of the vehicle. The projection of the barrel outside the hull made manoeuvring in the confined areas more difficult and limited the ability to drive across-country (due to barrel hitting the ground), and in wooded areas. The centre of gravity was transferred forward, which led to the overloading of front road wheels and consequently causing damage to the running gear and suspension. Finally, there was no satisfactory locking device to immobilise the barrel while on the move. At the same time, improved armour protection on German AFVs called for an increase in firepower of Soviet tanks and SP-guns. This brought about the introduction of more powerful guns with longer barrels, up to the point where utilising the basic elements of T-34 tank was no longer practical. A hull with a completely new layout was required. In the summer of 1944, work on the new layout started simultaneously with production of SU-100 in the UZTM. By the end of 1944, N. V. Kurin, the designer, developed a number of basic designs for new SP-guns utilising hulls of all currently available Soviet tanks — as they were designed and also with redesigned the layouts. In October 1944, the UZTM submitted five designs for review by Technical Council of NKTP:
— SU-122P, armed with the 122mm gun D-25S, at that time cast in metal and successfully undergoing plant trials;
— ESU-100, armed with the 100mm gun D-10S, with the crew compartment at the rear and electric transmission;
— SU-100-M-1, armed with the 100mm gun D-10S, fitted onto the hull of T-34 tank. The crew compartment was moved to the rear, whilst the engine and transmission unit were moved forward;
— SU-100-M-2, armed with the 100mm gun D-10S, based on the T-44 tank with the crew compartment at the rear;
— SU-122-44, armed with the 122mm gun D-25-44S, utilising the hull and systems of the T-44 tank and having the crew compartment in the front. The Technical Council considered the SU-100-M-2 and SU-122–44 as the best. By Decree No.625, of the NKTP 26th October 1944, UZTM was to complete the design, prepare workshop drawings and manufacture experimental units of the SU-100-M-2 and SU-122–44. In December 1944, whilst undertaking detailed design work on the SU-122–44, it became obvious that, due to the 5 metre long barrel, its weight and dimensions were excessive. At the same time, the SU-100-M-2 with a crew compartment at the rear, was shorter in length and the total weight, including increased armour, was in line with other vehicles of its class. Based on the results, it was decided to proceed with work only on the SU-100-M-2, whilst work on the SU-122–44 was halted by the Directive No.107 of the NKTP dated 7th March 1945. The same directive allocated the name «Uralmash-1» and set the date of 1st May 1945 for the first trial unit to be ready. It is worth mentioning that the « Uralmash-1» design SP-gun was prepared by the design section of UZTM headed by L. Gorlitskiy in August 1943. However, it was not approved by the NKTP and was left «frozen» for a while. A.M. Lechtcind, I. I. Emmanuilov, A. G. Gaivaronskiy, G. F. Ksyunin, I. F. Vakhrushev, L. A. Pinus, E. A. Karlinskiy, E. I. Linkov, D. A. Geriev, V. L. Likhomanov, N. N. Efimov, A.D Nekhludov and others contributed to the design, and the head designer was L. I. Gorlitskiy. During March and April 1945, the two experimental vehicles were completed. One, designated SU-101, had the D-10S 100mm gun, the other, SU-102, was armed with the D-25S-44 122mm gun. By the end of the Great Patriotic War, these two units and one unarmed hull for testing the armour protection were completed. The « Uralmash-1» was an example of the SP-gun with a fully enclosed crew compartment at the rear and power/transmission unit at the front. In contemporary documents, it was often named as «of Ferdinand type». The hull of the SP-gun was made of welded rolled steel plates sloped to increase protection. The thickness of the hull front plate was 90mm at an of angle 27°; the crew compartment was protected by 122mm thick plate set at an of angle 35°. Side armour was 75mm thick, while rear armour plate was 40mm thick. The plates of the hull and crew compartment were combined at the rear. On the right side, there was a square armoured hatch. In the top of crew compartment, there was a circular rotating hatch fitted with a commander's observation sight. The D-10S gun was fitted in the solid mantlet in front plate of the crew compartment The barrel overhung the hull by 630 mm. The gun could be elevated between +18° and −2° in vertical plane, and traversed 22.5°. Thirty-five fixed ammunition rounds were provided. A telescopic sight TSh-19 and panoramic viewer were installed. The 12.7mm DShK anti-aircraft machine-gun, with 450 rounds, was mounted near the top hatch. The V-2–44 engine was located lengthways, in the front and to the right of the hull. The driver was situated on the left side. The transmission system was borrowed from the T-34 tank, though a few changes were introduced. The torsion bar suspension was adopted from the T-44 tank. The drive sprocket was used from the T-34 tank. With a weight of 34.1 tonnes, the SP-gun was able to reach speeds up to 54 km/h. There was a four man crew. For outside communication, the 9-RS radio was provided and internally TPU-3bisF. The vehicle was also provided with a signal system and intercom linking the commander and driver. The SU-102 differed from the SU-101 by having a D-25S-44 122mm gun with a vertical elevation of between +18,5° −0° 24′, it could be traversed 19°. Due to the small size of crew compartment, the ammunition complement was only 28 fixed rounds (compared to the D-25 gun for JS-2 or JSU-122 which used separate loading shots). The weight increased marginally to 34.8 tonnes. In the summer and autumn 1945, factory trials of both vehicles took place. Some installations had to be adjusted or changed, in particular ventilation and engine cooling systems. The temperature in the driver and crew compartments was high, and as a result the driver's station had to be relocated. As a result of concentrated efforts by designers and fitters, the two experimental vehicles were made ready for field tests. The « Uralmash-1» SP-guns were superior to any other Soviet SP-guns. The new layout allowed them to make it more compact, improved manoeuvrability and drivability in rough terrain. Safety of the crew was enhanced with the provision of the rear hatch. Armoured protection was better due to the compact layout. High points were scored during field trials with artillery fire. According to the Special Commission report, the overall armour protection of « Uralmash-1» proved better than armour on any other Soviet tank and SP-gun, including the JS-2 and JSU-152! Equal load distribution on the road wheels reduced wear and tear. The location of the crew compartment to the rear, allowed the mounting of a very long barrelled cannon such as D-10 or D-25. On the negative side, the crew compartment was smaller than in the SU-100 and, despite improvements introduced to engine cooling system, conditions for the driver were extremely hard, and in hot days unbearable! Gunfire affected the integrity of the crew compartment top plate, especially in the SU-102. Both SP-guns hurriedly passed their tests and were recommended for acceptance into service. Nevertheless, they were not accepted. There were many reasons, the end of the war, demobilization, and an excessive number of already manufactured SP-guns. However, I believe the main reason was the introduction of the T-54 Main Battle Tank with its 100mm gun, that led to termination of work on « Uralmash-1». At present, an SU-101 is displayed in the Military Historical Museum of Tank Arms and Technology in Kubinka. Translated by: Krzysztof Pawlowski
Proof-read by: Chris Amundson
Sources: «Modelist-Konstruktor» No.2, 2001;
S. Gryankin «The T-44», a historical issue of the «Tankomaster»
M. Baryatinsky «Soviet tanks of the World War Two», 1995
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