Object 705 (Tank-705)

Soviet Union (1945-1948)
Heavy Tank – None Built

Background

In the latter stages of the Second World War, a great deal of Soviet tank design focused on improving existing heavy tanks, such as the IS-2, and building entirely new designs. This resulted in a number designs, with various degrees of performance and success, such as the IS-6 and IS-3.

After the discovery of the Maus and an in-depth look at German projects, the Soviets thought that the new imminent war against the West would require serious heavy tanks, with more armor and better guns than what they currently had. So, on 11th June, 1945, the GABTU (Main Directorate of Armored Forces) requested the development of new heavy tanks armed with the 130 mm S-26 gun, weighing 60 tonnes, and using torsion bar suspension. This led to a series of complex heavy tank and SPG designs, which would eventually lead to the heaviest Soviet tank of all time – the IS-7.

Developed and built at Kirov plant Leningrad after almost 5 years of development, the IS-7 is often regarded as the peak of heavy tank design. However, the Soviets officials’ displeasure with such heavy vehicles led to the cancellation of design and development of all AFVs weighing over 50 tonnes. The act came into practice at the meeting of Ministers of the Soviet Union on 18th February 1949, ending the IS-7’s life.

But few know of the other Kirov plant’s design, meant as a rival to the IS-7 (Object 260). Kirov Chelyabinsk (ChKZ) and Kirov Leningrad (LKZ) had been rivals for years, and so there are many parallel projects by the two factories. Their design was called Tank-705 as per the blueprints, but would eventually be known as the Object 705. The project started in June 1945 and was terminated in 1948, alongside other heavy tanks.

Development first began in June 1945, immediately after the discovery and analysis of German heavy AFVs. This triggered a series of projects over several design bureaus and factories. For ChKZ, the IS-3 was proving to be a success, and the IS-4 (Object 701) was soon to enter production. In contrast, LKZ had just lost several programs, most importantly, the IS-6. But the experience gained from it led to a series of promising designs. Fast forward a couple of years, and LKZ had full-scale mock-ups of one of the best heavy tanks ever designed, and was beginning prototype production. Meanwhile, Chelyabinsk and its design institute, SKB-2, had a series of disappointments, especially in the IS-4. In parallel, ChKZ had been working on the Object 705 and 718 (also called Object 705A) designs, but, as they were not deemed crucial or urgent, progress was slow. Further problems came with the 80th order on 2nd April, 1946 from V.A. Malyshev, when the mass of heavy tanks was limited to 65 tonnes. While the Object 705 still fit the criteria, the Object 718 did not. Yet work continued regardless.

Design

All that remains of the Object 705 are two drawings, one general silhouette and one detailing the armor profile and thickness. The tank was meant to weigh around 65 tonnes, use heavily sloped armor plates, and mount a thick cast turret mounted to the rear. This was done not only to use the engine as protection, but to also offset the length of the gun. What exact engine it would have used is unknown, but likely one between 750 and 1,000 hp for it to reach the expected 40 km/h. The transmission was a planetary automatic design. It is important to highlight is the sheer size of the tank design, being 3.6 m wide and 7.1 m long (just the hull), dwarfing the IS-4 (6,682 (hull only) x 3.26 x 2.4 m).

The crew was probably of 4: commander, gunner, loader, and driver. The crew were all situated inside the turret, with the gunner on the left side of the gun, the loader behind, and the commander on the opposite side. The driver was placed inside the turret, and would have a pivoting station, which allowed to always face the front of the hull. This was not the first, nor last, time Soviet designers would try to incorporate this idea. Two of the periscopes were mounted on the turret roof, the one on the left side was to be used by the commander and the one on the right was to be used by the loader. The driver also had his own periscope, but mounted further forwards. The gunner likely did not have his own periscope, and had to rely on his sight and/or crew callouts.

Armament

In terms of main armament, it is uncertain what the Object 705 would have used. Some sources claim it was a high-power 122 mm gun, while others state directly that it was a BL-13 122 mm gun. This was no new and revolutionary gun by the late 1940s, it was actually developed by OKB-172 in 1944, with several upgrades made later, such as the BL-13T and BL-13-1. The rate of fire varied between the different versions of the gun, as the upgraded variants had a mechanical gun rammer, but it was between 5 to 10 rounds per minute. Such long reload times were caused by the two-part ammunition. Secondary armament consisted of a coaxial 12.7 mm DhSK heavy machine gun mounted on the right side of the gun and potentially a roof-mounted DhSK.

However, a larger caliber gun (130 mm) is not entirely out of the equation, as later IS-7 designs used such a caliber, and the diameter of the barrel on the silhouette of the tank is thicker than that of a 122 mm gun. To back this theory up, on 11th June, 1945, specifications clearly stated that the gun on the new heavy tank should be a 130 mm S-26, the land version of the naval B-13. At the same time, the BL-13 was already deemed obsolete when facing German heavy tanks.

The S-26 was developed between 1944 and 1945 at TsAKB by head engineer V.G. Grabin. It was largely based on the B-13 130 mm naval gun (not to be confused with the previously discussed BL-13) with a semi-automatic horizontal sliding breech lock, slotted muzzle-brake, and barrel smoke evacuator. Rate of fire was around 6 to 8 rounds per minute. The shells weighed 33,4 kg and had a muzzle velocity of 900 m/s.

Ammunition was stored along the angled sidewalls, a solution present on most Soviet tanks with angled sidewalls. The exact number of rounds stowed is hard to estimate, but most tanks using similar guns carried around 30, split into charges and projectiles.

Armor

A study of the drawing showcases the armor thickness and the complex arrangement of the armor plates. The upper frontal plate consists of one 140 mm thick plate, angled at 60°. On the top corners, it is met by a plate angled upwards across the upper side of the engine bay. The lower plate is also 140 mm, angled 55º from the y-axis. In terms of side armor, a very interesting idea was adopted. The two 130 mm armored side walls were brought inwards at a steep 57° angle, creating a diamond-like shape from the front. SKB-2 had used angled walls on the IS-3, but only on a minimal level for more interior space. Instead, such diamond-shaped sides were first used by the Kirov Leningrad plant on the first IS-7 design, the Object 257. This option provided excellent side protection from conventional projectiles, but also increased mine resistance, as the blast force was directed outwards. All this came as a trade-off for interior space. A major issue with this design feature is the narrow-angle created at the bottom of the tank. This space is very hard to use, and essential components like engine and transmission have to be moved up, making the tank taller. Another big issue was the suspension, namely where exactly to put it. On the Object 257, the issue was resolved by designing a brand new external suspension, using volute spring bogies like on the Sherman tank. The exact solution on the Object 705 is, naturally, unknown, but a handful of different options could have been used.

The turret was rounded and flat, creating angles between 50º and 57º. Armor varied greatly depending on the strike face, with the thickest front part being 140 mm and the thinnest roof section being 20 mm.

Roadwheels and Suspension

One of the most curious aspects of the design was its wheels. Seven large steel-rimmed wheels per side were used. A hint comes from SKB-2’s other super heavy tank project at the time, the massive 4-tracked Object 726 behemoth, which featured among other wheel and suspension ideas, large, steel rimmed roadwheels. There is a serious possibility of them being used on the Object 705 as well. These wheels would later become a mainstay in heavier ChKZ designs, such as the Objects 752, 757, 770, and 777, the latter two using hydropneumatic suspensions.

Yet blueprints of the Object 718 show a slightly different set of wheels. These were drawn as steel rimmed and with deep spacing between the rims and rest of the stapled steel lids. The wheels seem to have been mostly unique to the Object 705A. The Object 705 could have used the same wheel design or something else, as the lower weight allowed for more playroom in terms of weight thresholds on the components.

Implementing conventional torsion bars running across the length of the hull initially seems challenging due to the hull floor being so narrow, due to the inwards angled side walls. Yet the simple solution to this was that the tank hull was simply very wide. This allowed the side walls to keep a steep angle while still allowing for a sufficiently long torsion bar to be mounted. Such issues had been encountered by Soviet engineers both previously and later, with a variety of solutions such as bundled torsion bars, lifting the torsion bars higher up into the hull, or moving the torsion arm on the outside of the wheel.

Object 705A

At some point during the development of the Object 705, an even heavier variant was designed. It would have weighed 100 tonnes and be armed with the 152 mm M-51. Just the mass alone would place the Object 705A as one of the heaviest Soviet tanks designed post-war. Yet blueprints only show specific details, such as the turret, suspension, roadwheels, and transmission. A lack of hull blueprint makes it hard to legitimize it as a complete design, and it is entirely possible that its hull never got drawn to begin with. This naturally leaves the proposal in a lot of mystery and up to significant speculation.

Conclusion – Weight Shaming

With so little information available, it is hard to properly judge the capabilities of the Object 705 and 718, even when compared to the different variations of the IS-7. The vehicles were likely designed between 1947 and 1948, at which point the BL-13 was already outclassed (Kirov Leningrad had used it on the IS-6 and other projects in 1945). So, in that respect, the Object 705 fell behind the IS-7. Yet in terms of armor, it was on par, if not even better protected than the most advanced IS-7 variant. As for the Object 718, the lack of information prevents any conclusions to be drawn, with the one and main issue being the weight of 100 tonnes. When discussing both the Object 260s and Object 705s, it is generally clear that such heavy vehicles could prove vulnerable and simply too heavy for effective battlefield use. The heaviest Soviet tank in service, the IS-4, weighed 53 tonnes and was still considered overweight and too slow. Thus it seems almost natural that the Soviet government saw the limitations and waste of resources devoted to such heavy vehicles. The final nail in the coffin for these designs was the cancellation of all AFVs above 50 tonnes on 18th February, 1949.

Object 705 specifications
Dimensions (L-W-H)	7.1 – 3.6 – 2.4 m
Total Weight, Battle Ready	65 tonnes
Crew	4 (Commander, Gunner, Driver & Loader))
Propulsion	1,000 hp engine of unknown type
Speed	40 km/h (hypothetical)h
Armament	130 mm S-26 or 122 mm BL-13 gun coaxial 12.7 mm DShK heavy machine gun
Armor	Hull armor: Front top plate: 140 mm at 55° Front bottom plate: 140 mm at -50° Side plate: 100 mm at 57° Top: 20 mm Belly: 20 mm
Total Production	Blueprints only

Sources

Domestic armored vehicles 1945-1965 Soljankin, A.G., Pavlov, M.V., Pavlov, I.V., Zheltov
TiV No.10 2014 A.G., Pavlov, M.V., Pavlov
TiV No. 09 2013 A.G., Pavlov, M.V., Pavlov
https://yuripasholok.livejournal.com/2403336.html
The genius of Soviet artillery. Triumph and tragedy of V. Grabin – Shirokorad Alexander Borisovich