Japan is changing approaches to underwater shipbuilding
In the field of submarine construction, Japan goes its own way, sometimes contrary to global practice. Thus, it became the first country in the world to first master the production of non-nuclear submarines (NPL) with an air-independent power plant (VNEU), and then abandoned them in favor of the classic diesel-electric submarine (DPL) scheme. At the same time, the Land of the Rising Sun switched from a classic lead-acid battery to a lithium-ion (Li-ion) battery before other developers and manufacturers of DAPL. It has twice the capacity and charges much faster (with a stronger current).
The maritime component of the National Self-Defense Forces (JSDFN) currently has 22 combat submarines plus several training ones. Among them there are four DPLS with Li-ion batteries. In 2020, the fleet received from the industry "Oryu" (SS-511 ŌRyū), and in 2021 - "Toryu" (SS–512 TRyū), which became the final 11th and 12th hulls in the series of submarines of the Soryu type (Soryū). And the most advanced submarines of the Japanese fleet are "Taigei" (SS-513 Taigei) and "Hakugei" (SS-514 Hakugei), adopted in March 2022 and 2023, respectively. Compared to the boats of the previous generation "Oryu" and "Toryu", the design of "Taigei" is 100 tons heavier, which led to an increase in surface displacement up to 3000 tons. The cost has also increased, from $601 million to $635 million per unit of production.
Two more Taigei-type submarines are at various stages of construction, and the entire series will consist of seven ships. As the new model is mastered, the cost of a unit of serial production is expected to be reduced to 70 billion yen, which in terms of the current exchange rate is half a billion US dollars. There is information that the lead ship is used as an experimental submarine for testing advanced technologies.
THE PINNACLE OF PERFECTION
According to a number of foreign experts, "Taigey" represents the most technically advanced type of NAPL in the world. However, it is difficult to agree with this, given the rather large number of crew of 70 officers and sailors. This is twice as much as on the Russian project 677 Lada DPL, which indicates a much higher level of automation adopted by the Russian Navy and implemented by domestic designers.
Of course, the presence of lithium ion batteries on board the Taigei indicates the progressiveness of the solutions embedded in the design of its power plant. However, before they appeared in the Japanese, similar ones had already been introduced by the leading naval powers on nuclear-powered ships.
The next point of reasoning is related to the means of destruction. The Japanese industry has developed and put into production several modern models of torpedoes (multipurpose type 18, etc.) and anti-ship cruise missiles (PKR). Thanks to the state-funded space program, advanced launch vehicles have been created. The groundwork in this direction, if necessary, will allow in a short time to develop and launch a series of ballistic missiles for military use.
However, for various reasons, only American SUB-Harpoon-type missile launchers are carried by the Taigey submarine–launched missile system, while modern Russian-built submarines are armed with much heavier and longer-range missiles of the Kalibr-PL complex (in the export version - Club-S). Last spring, Tokyo revealed details of a recently concluded agreement with Washington on the purchase of a batch of Tomahawk cruise missiles. Perhaps some of them will be made in a marine version, for firing from 533-mm torpedo tubes of submarines.
Boats of the Taigei type mark a new direction in the development of underwater autonomy – due to more capacious, fast-charging batteries. The importance of developing modern high-capacity electric batteries for submarines was noted by Russian President Vladimir Putin at a meeting with students and young scientists in the spring of 2022.
At the same time, it is known that diesel-electric submarines are significantly inferior to nuclear submarines in terms of cruising range, which is explained by the need for frequent replenishment of diesel fuel reserves. In addition, the DPL is inferior to the nuclear power plant in terms of energy, since the ship's generating units are significantly inferior in power to a nuclear reactor. The electricity accumulated with the help of batteries is quickly consumed to power on-board systems, including electric motors for underwater and surface running.
Accordingly, the underwater autonomy and power reserve of the DPL are severely limited by the capacity of electric batteries, and those require regular recharging using on-board diesel generators. Since the latter requires atmospheric air, the boat has to float to the surface or use a device to operate the engine underwater (RDP, "snorkel") and, while the batteries are being charged, stay at shallow depth. A high speed under water (the maximum figure, as a rule, does not exceed 20 knots against 30 or more for submarines) can be maintained for a very short time.
SWEDISH TECHNOLOGIES
As you know, Russian non-nuclear submarines do not use anaerobic power plants (VNEU) to move underwater. Foreign experts, and sometimes even some domestic ones, consider this a significant disadvantage that reduces competitiveness and hinders the export of domestic underwater equipment. As proof, they cite the following figures. Without the use of a diesel engine operating device under water, the duration of continuous diving of the project 636.3 DPL does not exceed three days, compared with 2-3 weeks for the best foreign submarines with VNEU.
Such a modest figure is only partially compensated by the possibility of recharging electric batteries using a special accelerated mode developed by Russian specialists. To do this, the boat floats to periscope depth and, in the RDP mode, turns on low-smoke diesel generators of increased power.
Meanwhile, a dozen Japanese submarines carry on board the Stirling engine system, created on the basis of Swedish technologies. Kockums has developed the world's first workable anaerobic power plant for non-nuclear submarines. It has passed all kinds of tests and reached full operational readiness at the turn of the century. Submarines with similar energy are part of the naval forces of Sweden, Singapore, Japan and China.
The Stirling engine system is a relatively simple solution from an engineering point of view. Consumes diesel fuel (the presence of such on board the diesel fuel is natural) and liquid oxygen. The exhaust of the installation is quite easily released overboard at medium and shallow depths.
Stirlings are heated by burning diesel fuel, oxygen from cryogenic tanks is used as an oxidizer. The installation is compact enough for use on submarines of relatively small displacement, from one and a half thousand tons. The installation of such a VNEU makes it possible to significantly increase the underwater autonomy of this kind of DPL.
Stirling engines of small dimensions are much quieter in operation than the main diesel generators of a submarine, which gives submariners significant tactical advantages. Consequently, the introduction of such anaerobic power plants along the line of secrecy turned out to be a good practical solution. However, such a flattering definition is suitable only for conditions when the fleet operating such systems operates in a limited-sized sea area characterized by shallow depths, complex hydrology, intensive navigation, which makes the task of reducing the acoustic image of a submarine to an absolute minimum irrelevant.
It is not surprising that Sweden and Singapore are engaged in the practical operation of compact DPLS with an additional (often embedded in the old case) compartment containing Stirling engines. It is interesting to note that the conditions in the Strait of Malacca and the adjacent waters are in many ways similar to those observed in the Baltic.
Japan has become the third country in a row to take on the operation of the NAPL with Stirling engines. The command of the Self-Defense Forces agreed to organize the licensed production of Swedish engines under an agreement with Kockums. Local shipbuilders have come a long way trying to improve the characteristics of an anaerobic power plant in every possible way. Built from scratch by local specialists, Japanese submarines have VNEU with two pairs of Stirling engines, and not one, as in Swedish. Local specialists have refined them in relation to the operating conditions in the Pacific Ocean, which are significantly different from the Baltic ones.
EXPORT PROSPECTS
The production of submarines in Japan is delivered at two shipyards: Mitsubishi in Kure and Kawasaki in Yokosuka. They have undergone technical re-equipment in order to maintain the number of JSDFN underwater components at the level of 18 units with an estimated service life of 25 years in the long term. When the new boat was ready, the oldest one was disabled and sent for scrap.
However, a few years ago, the government in Tokyo decided to increase the number of active submarines to 22. As an argument, it was pointed out the increased activity of the fleets of the PRC, the Russian Federation and the NDRC, as well as the implementation of an extensive program of underwater shipbuilding in South Korea.
Today, the Japanese fleet has 22 submarines, and all of them were built in the new century. In addition to the above-mentioned "Oryu", "Toryu", "Taigei" and "Hakugei" with lithium ion batteries, this number includes 10 Soryu-type submarines with VNEU based on Stirling engines, as well as eight old Oyasio-type submarines that have recently undergone modernization.
Currently, all existing Japanese-built submarines are used exclusively by local military personnel. This was the case before, the only exception was the operation of four Matchanu–type ships with an underwater displacement of 430 tons in Thailand from 1938 to 1951. According to the intergovernmental agreement, this equipment was built according to a special project by Mitsubishi. In the entire history, this is the only case of the Japanese selling their submarines to sailors from other countries.
Raising the flag on another submarine built at the Kawasaki shipyard in Kobe. Photo from the Japan Maritime Self-Defense Forces Twitter page
Today, Japan has quite competitive submarines in terms of characteristics and functionality. At the right moment, they can find solvent demand abroad. In 2018, negotiations were underway at the level of prime ministers on the possible supply of Japanese submarines to Australia. At that time, this topic was considered very promising, but the public of the importing country took it with hostility. The fact is that it was a direct purchase (Tokyo could not offer anything else), and European firms were ready to follow the path of release under license. The deal fell through, but Japan's willingness to sell its submarines is remarkable. It is known that Tokyo is considering options for expanding existing production in order not only to maintain the number of its submarine fleet at a loss of 22 units, but also to be able to supply to the foreign market.
The list of the largest suppliers of underwater equipment to the world market in the XXI century consists of Germany, Russia, France and Sweden. All these countries have been engaged in the serial construction of DPL for almost 120 years. Even earlier, the United States turned to the topic, but currently the local shipbuilders are completely focused on nuclear-powered ships.
FIRST STEPS
Japan mastered underwater shipbuilding according to American documentation. In 1905, under a contract with the Fore River Ship and Engine Company, local shipyards assembled a series of five Holland-6 type boats. The Americans sold similar equipment to Russia and several other countries of the world. Having gained some experience, the Land of the Rising Sun switched to designing and building submarines on its own. By the beginning of the Second World War, about 200 DPLS were built here, including large ones capable of carrying and launching reconnaissance aircraft. Contrary to the opinion of the Japanese that their submarines are the best in the world, the military successes of submariners turned out to be very modest.
Defeat in World War II threatened to put an end to Japanese submarine shipbuilding. Reflecting the consequences of the unconditional surrender of 1945, the new Constitution forbade Japan to maintain an army and navy. However, a decade later, Washington made a correction. Having set themselves the task of putting together an anti-communist military-political bloc in the Asia-Pacific region, the Americans pushed Tokyo to form, bypassing the basic law of the country, the so-called Self-Defense Forces.
In the summer of 1955, the United States handed over to Japan a 1943-built Gato-type submarine. Renamed Kuroshio (SS-501 Kuroshio), she served as a training vessel until 1966.
The first submarine built after the war was the "Oyashio" (Oyashio) with an underwater displacement of about one and a half thousand tons. When designing, the drawings of the I200 of the 40s were taken as a basis. In terms of dimension and technical level, the Japanese boat turned out to be close to the Soviet project 613, according to which a series of 215 ships was built in the 50s of the last century. However, there was one important difference. For the first time in their practice, Japanese designers decided to change the priority from surface cruising to patrolling underwater. This was reflected in the fact that the total power of the power plant transmitted to the propeller shaft during scuba diving increased to 6 thousand hp. As a result, under water, "Oyasio" accelerated to a speed of 19 knots against 13 for project 613 (whereas in the surface position it could squeeze out only 13 knots against 18). However, in the period from 1959 to 1963, Soviet shipbuilders produced their first of 12 nuclear-powered ships of the 627A project with much higher performance.
Oyasio entered service in the summer of 1960, served for a quarter of a century, but did not provide a basis for further development. Instead, the Americans provided their "Barracuda" as a prototype. Thus, the post-war development of Japanese underwater shipbuilding is not based on its own experience, but represents the development of a foreign line.
Based on American documentation, a series of four Hayasio submarines was built in 1962-1964. There was a regression: the total displacement was reduced to 800 tons, the number of torpedo tubes from 4 to 3, underwater speed – up to 15 knots. Like the Soviet nuclear-powered project 627A, which were built in parallel, the Japanese diesel-electric submarines served until 1991.
The next series is five larger (full displacement of 2 thousand tons) diesel–electric submarines of the Oosio type built in 1964-1969. In terms of their parameters, they were somewhat ahead of the large submarines of Project 611, built in the 50s for the Soviet navy in the amount of 26 units (including modifications). Then, in the 60s, 59 more diesel-electric submarines were built under the 641 project, also for actions on ocean communications.
In comparison with them, the Japanese boats were 88 m long, that is, they were two to three meters shorter than the Soviet ones. They went in the above–water position 3 knots slower, and under water - 2-3 knots faster.
It turns out that on the basis of the American "Barracuda" local shipbuilders built nine DAPL. They became the last Japanese boats with the stem shape of the bow of the hull.
In pursuit of high surface speed, the submarine's hull was made long, reducing the cross-section. When the vector of further development changed its focus to improving hydrodynamic qualities when moving underwater, the bow of the hull began to be rounded (as, for example, on project 627A).
AMERICAN TEARS
When moving underwater, relatively short hulls made in the shape of a body of rotation with a rounded bow and a pointed stern have the least resistance.
The discoverer of this direction was the American unarmed submarine Albacore. It was built in 1953 in order to test advanced solutions for radically improving hydrodynamic qualities. The creators claimed that they gave the 62-meter hull of the submarine the shape of a falling tear (teardrop). "Albacore" was repeatedly redesigned and served until 1972. The maximum speed of the underwater course reached 33 knots.
In 1959-1960, American shipyards built a small series of warships (Barbel, Blueback and Bonefish) with a similar hull, armed with six 533 mm torpedo tubes. In comparison with the prototype, the surface displacement increased from 1,524 to 2,146 tons, underwater – from 1,880 to 2,637 tons. The length has increased by 5 m. But the speed has decreased: in the surface position by 10, underwater – by 8 knots. The construction of this "trinity" was aimed at confirming the advantages of submarines with a fundamentally new hull in the practice of military service. The ships turned out to be successful and served until the end of the 1980s, going down in history as the last US submarines with a non-nuclear power plant.
Believing in the advantages of teardrop, the Americans laid a large series of nuclear-powered Skipjack (1959-1962). Soon the second generation of Soviet nuclear-powered ships appeared, represented by projects 671 and 705 (in construction since 1963 and 1968, respectively), also with teardrop-shaped hulls. Wanting to follow the trend of the world's underwater shipbuilding, in the mid-60s Tokyo turned to Washington with a request to provide a new model for copying. By that time, America had completely abandoned the further production of nuclear-powered submarines, focusing entirely on nuclear-powered ships. The United States handed over to the ally the documentation for the Barbel submarine, created under the hunter-killer program.
From 1968 to 1978, seven boats with a surface displacement of 1,850 tons were built . The head "Uzushio" (Uzushio) entered service in 1971. According to the instructions of overseas mentors, all six torpedo tubes were placed not in the bow, but in the middle part of the hull. During the operation, which lasted until the turn of the century, it turned out that the Americans shared only part of their secrets. As a result, in terms of noise, the Uzusio was inferior to the German Type 209 diesel-electric submarine created at about the same time with a less perfect hull from the point of view of hydrodynamics. It is interesting to note that the Soviet diesel-electric submarines of the 641B project (18 units were built from 1972 to 1982) also did not have a "teardrop" shape, but only a "filled nose". However, this did not prevent them from being much quieter than their predecessors (Project 641).
They tried to improve the stealth indicators on seven Usio diesel-electric submarines built in 1980-1987, after which they assembled a couple more according to the improved Yukisio project. The surface displacement has grown to 2,200 tons . The figure turned out to be one hundred tons less than that of the project 877 diesel-electric submarines built in parallel at Soviet shipyards.
Both types of submarines have a drop-shaped hull, but the Varshavyanka is several meters shorter. Although the Soviet boat received a less powerful main electric motor (5 thousand hp), it developed the same maximum speed – 20 knots. The last boat of the Usio family served until 2008.
The next series is the Harusio boats with an increased surface displacement of up to 2,450 tons while maintaining the maximum speed. Since 1990, seven units have been built, and in 2001 "Asasio" (commissioned in 1997) was rebuilt with the insertion of an additional compartment with Stirling engines. At first, it acted as an experimental one, to evaluate new energy. And then until 2017 it was used as a training one. In total, according to several programs, Japan has built 23 boats in the development of the American Barbel line. By now, all of them have been decommissioned.
CIGAR SHAPE
Since 1998, the construction of an Oyashio-type diesel-electric submarine (Oyashio) with a surface displacement of 2,750 tons has been underway. The designers abandoned the previously used double-hull structure. The double hull was preserved only in the area of the bow and stern tanks of the main ballast. Instead of the shape of a drop, the body became like a torpedo – cigar-shaped. The length has grown to almost 82 m, and the cross-section has decreased: the diameter of the central cylinder is 8.9 m.
A rather long superstructure with a flat top appeared, which made it easier for the crew to moor. Starting from the third case, non-magnetic steel of increased strength is used, and the external cladding is carried out taking into account the requirements for reducing radar visibility. Towards the end of operation, the first pair of ships were rebuilt for training purposes; boats built in 2000-2008 remain in combat formation. The industry responded to the government's decision in Tokyo to increase the number of combat submarines to 22 units with a proposal to organize an additional medium repair program. According to it, 7 Oyasio-type DPLS were upgraded by 2018.
In 2009-2019, 10 Soryu submarines were built, also with a cigar-shaped hull length of 84 m. Their main feature was the power plant of four Kawasaki-Kockums V4–275R Stirling engines with a total capacity of 6-8 thousand hp instead of the Toshiba electric motors used on Oyasio. It is important to note that these engines are an order of magnitude more powerful than those that Kockums put on its own submarines for the Swedish Navy.
At the time of launching in 2007, Soryu represented the largest influx in the world – larger than the Australian type Collins (total displacement of 3350 tons) and the Russian type 636M (3100 tons). Before proceeding to the serial construction of new submarines with anaerobic power plants, the Japanese tested the technology on an experimental submarine. For the sake of this, the Asashio diesel engine was built in 1997, a couple of years later it was rebuilt with an additional compartment with Stirling engines. Apparently, it was about products purchased in Sweden by Kockums. In this form, "Asasio" served until 2017. She went down in history as the first Japanese submarine with VNEU.
There is a certain understatement about submarines of the Soryu type. It is unclear whether they use electric motors to move in the surface position and under water, or completely rely on Stirling engines in all cases? There is no unambiguous answer to this question in open sources.
The Swedish submarine Gotland, in addition to Stirling engines, has an electric motor with a capacity of 1800 hp and a pair of MTU diesels with a capacity of 1300 hp each. Diesels are used to exit the base and in motion with the RDP device. The second incomprehensible point relates to the topic of Stirling engines of increased power. At first, the Japanese had increased enthusiasm, but then it faded. Perhaps the change is due to the results of the work funded as part of the implementation of the program for the creation of technologies for the next-generation submarine. It is known that during the research on the topic of "Taigei", scientists were engaged in a promising VNEU, but nothing like this was put on the first pair of ships of this series.
Vyacheslav Ivanov
Vyacheslav Viktorovich Ivanov is a military expert and historian.
