2B1 "Oka" ("Transformer") Mortar
Self-propelled mortar 2B1 "Oka" was developed in the middle of the 1950s simultaneously in two design bureaus: the artillery unit was engaged in Kolomenskoye SKV engineering, and the chassis "object 273" - KB of the Kirov plant in Leningrad. In total, the Kirov plant built four self-propelled units 2B1. The 420 mm mortar was intended for firing a 750-kilogram nuclear bomb at a distance of up to 45 kilometers. The origin of the name comes from the tributary Oka river in the Volga River.
The weight of the self-propelled gun was more than 55 tons, and the length of the smooth barrel was almost 20 meters. As the main weapon was a 420-mm smooth-bore mortar 2B2 in length of 47.5 calibers. Loading shells was carried out from the breech of the mortar with a crane (min. 750 kg), which adversely affected its rate of fire, only 1 shot in 5 minutes. The ammunition of the 2B1 Oka mortar contained only a nuclear warhead, which guaranteed at least one tactical nuclear strike in any circumstances. The vertical angle of the mortar was lying in the range from +50 to +75 degrees. In the vertical plane, the barrel moved due to the hydraulic system, while the horizontal guidance of the mortar was carried out in 2 stages: the initial rough adjustment of the entire installation and only after that the guidance on the target with the help of an electric drive.
During the march, the self-propelled mortar was driven only by the driver, while the rest of the crew (7 people) was transported separately on an armored personnel carrier or truck. In the front part of the machine's housing there was a MTO - engine-transmission compartment, in which a 12-cylinder liquid-cooled V-12-6B diesel engine equipped with a turbocharger system and developing a power of 750 hp was installed. There was also a mechanical planetary transmission, which was interlocked with a turning mechanism.
The power plant of the heavy machine was borrowed from the T-10 tank. The running gear of the machine, designed by KB of the Kirov plant, according to the GBTU classification, received the designation "Object 273". This chassis was maximally unified with SAU 2A3 and met the increased requirements imposed on the strength of the structure. On this chassis, a power plant was used from the Soviet heavy T-10 tank. The chassis of the self-propelled mortar "Oka" had 8 twin support rollers and 4 supporting rollers (on each side of the body), the rear wheel was a guide, the front wheel was the guide wheel. The steering wheels of the chassis had a hydraulic system lowering them in the fighting position on the ground.
Suspension of the chassis was torsion beam with hydraulic shock absorbers, which were able to absorb a significant part of the recoil energy at the moment of a mortar shot. However, this was not enough. There was also a lack of anti-recoil spades ["chopping devices"] on the mortar. For this reason, when firing a 420 mm mortar, the mortar drove away on the tracks back to a distance of 5 meters. Because of the difficulty of loading the winged shell from the breech, the rate of fire of the gun did not exceed 1 shot in 5 minutes. In the marching position, the self-propelled mortar was operated only by the driver-mechanic-the rest of the crew was carried by a truck or armored personnel carrier.
On November 7, 1957, at the military parade in Moscow, the Oka was first shown to the international public together with a 406 mm self-propelled gun on the same chassis. The demonstration of these huge guns made a furor among foreign journalists and domestic inhabitants. Some foreign experts expressed the opinion that the artillery shown on Red Square is just a sham designed for an intimidating effect. They were not far from the truth.
During mortar tests, when conventional ammunition was fired, there were various breakages. During the tests, it was noted that when firing ordinary mines can not withstand sloths, the gearbox was torn from its place, there were destruction of the chassis structure, and there were other breakages and shortcomings. The completion of the self-propelled mortar 2B1 "Oka" was going on until 1960, when the Council of Ministers issued a decree on stopping work on this project and the self-propelled gun 2A3.
In the 1990s, a prototype vehicle was exhibited at the the St. Petersburg Artillery Museum. All who would be at the artillery museum in St. Petersburg, probably surprised by the size of the self-propelled mortar 2B1 "Oka", which is one of the most interesting exhibits of the exposition. Despite the failure with the Oka mortar, Soviet designers were able to use all the accumulated experience, including negative, in the design of similar artillery systems in the future. That, in turn, allowed them to reach a qualitatively new level of designing various self-propelled artillery systems.
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