Japanese secret of low-noise Russian submarines

The well-known American publication The National Interest in Russia in one of its materials told about how, thanks to the purchase of high-precision metal-cutting machines from the Japanese company “Toshiba” in the 1980s, the Soviet Navy (Navy) managed to overcome the traditional lag behind the United States in the field of stealth submarines.

At the same time, this topic is also very popular on various Russian Internet resources and in popular science publications, periodically appearing when it comes to the Soviet or modern Russian submarine fleet. Moreover, the submarines that were fitted with screws made on Japanese-made machines still form the basis of the grouping of multi-purpose nuclear submarine forces of the modern Russian Navy.

In most cases, the main conclusion drawn from the story of buying Japanese machine tools is the technological backwardness of the Soviet Union. Let’s try to figure out what really contributed to the Japanese machines in increasing the stealth of Soviet submarines?

Since the advent of nuclear submarines, Soviet submarines of this class have traditionally been inferior to those in us and British navies (with which the Americans shared their experience in this industry). The world’s first nuclear-powered submarine, the Nautilus, entered service in the US Navy in 1954, while the USSR’s first K-3 submarine was accepted into the Navy only in 1959. In addition, during this time, the United States quickly passed the stage of first-generation submarines, which were built according to the canons of diesel submarines, and began mass construction of second-generation submarines. In the USSR, second-generation nuclear submarines began to appear only in 1967.

In the 1960s and 70s, American submarines had a huge advantage over Soviet submarines. They had a significantly lower noise level and much more advanced sonar systems, which gave them an undeniable advantage in underwater warfare. This especially undermined the combat stability of the naval component of the Soviet strategic nuclear forces (SNF). Given that the range of Soviet sea-based ballistic missiles at that time was 2.5 thousand kilometers, the submarines needed to come close to the coast of the United States, and therefore to overcome the anti-submarine borders of NATO. At the same time, given the high noise level of Soviet submarines, American hunting boats could successfully track them.

As a result, in the 1970s, the Soviet Union began a large-scale program to overcome the lag of the Soviet submarine fleet from the American one, which consisted mainly of reducing the noise level of submarines. As a result, by the early 1980s, the Soviet submarine fleet had made a qualitative leap and reduced to a minimum the lag behind the American one. The new Soviet third-generation submarines-the multi-purpose submarines of projects 945 and 971, the submarines with cruise missiles of projects 949 and 949A, as well as the giant submarines of project, 941-had a much lower noise level than their predecessors. For example, submarines of project 971 (which form the basis of group modern multi-purpose submarines of the Russian Navy) are fully comparable in noise level with the American nuclear submarines of class “Los Angeles” (the most famous and mass third-generation nuclear submarine, before the submarine of the fourth generation, was considered to be the least noisy in its class). What made it possible to achieve such a significant qualitative leap in the field of creating submarines?

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In itself, the noise level of nuclear submarines is higher than that of diesel-electric submarines. First, one of the main sources of noise for nuclear power plants is the nuclear reactor, or rather the circulation pumps that provide the movement of the coolant through the reactor. Secondly, if diesel-electric submarines have a propeller-driven directly by an electric motor, then the reactor of the submarine provides rotation of the turbine, which through the gearbox provides rotation of the propeller. Therefore, the turbine with a gearbox and other mechanisms are a powerful source of the noise. Third, the source of increased noise is the screw itself. During the operation of the propeller at certain speeds, cavitation occurs, accompanied by a high sound level. In this case, cavitation occurs primarily at high speeds of the submarine, and the maximum stealth of the submarine is provided in the so-called creeping mode when the speed is limited to 5-10 knots. Finally, the sources of noise on a submarine are dozens of modes and mechanisms.

In the course of improving Soviet submarines, a wide variety of noise reduction measures were implemented. So, all the mechanisms of the boat were placed on shock-absorbing foundations and combined into so-called zonal blocks, which were isolated from the hull by pneumatic shock absorbers, which together formed a so-called system of two-stage noise and vibration isolation. Soviet third-generation submarines began to be equipped with OK-650 series reactors, which allowed the natural circulation of the coolant up to a third of the maximum power, which virtually eliminated the noise of the reactor in creeping mode. At the same time, in the course of solving the problem of increasing the level of secrecy of Soviet submarines, the level of mechanical engineering in the country as a whole was significantly raised. This, in turn, significantly reduced the noise from various mechanisms of the boat.

The acquisition of Japanese machines that made it possible to manufacture large-diameter propellers (up to 11 meters) with special saber-shaped blades and minimum tolerances, of course, had a huge impact on reducing the noise level of Soviet submarines. However, this well-known deal with the company “Toshiba” was important, but only one link in a colossal series of measures to improve the stealth of submarines. And it is unlikely that the acquisition of Japanese machines would have had an effect if the technological level of the Soviet industry was really backward.

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