The Sōryū-class, also known as 16SS-class, is one of the best diesel-electric attack
submarines in the world. These extremely silent and highly capable underwater vessels are
one of the most important chess pieces on the chessboard in the East Pacific. As the
Weapon Detective, we are investigating the Sōryū-class, the backbone of submarine forces
of the Japan Maritime Self-Defense Force. Please don't forget to subscribe to our channel,
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We may say, at first glance, the Sōryū-class is not sexy as the Izumo and Hyūga-class
helicopter destroyers or the P-1 maritime patrol aircraft. But, naval warfare has three
layers, which are surface, air and underwater. So, the submarines are as important as surface
combatants and aircraft for the Japan Maritime Self-Defense Force, shortly JMSDF.
The Japanese have always known that. As a matter of fact, their long-established submarine
tradition paved the way for the development of a good submarine like the Sōryū-class.
Japan acquired its first submarines during the 1904 Russo-Japanese War.
Until the Second World War, the Japanese had made important investments in underwater vessels.
Their qualities were high, but the navy had acquired them in an insufficient number. Besides,
during the war, the Imperial Japanese Navy used its submarines against the surface combatants
of the US Navy, not for the commerce raiding. So, the Japanese submarine operations were
not bright, like the German and the US. Still, the Japanese submarines managed to
sink three carriers, as well as some destroyers and cruisers.
One year after it was founded, the JMSDF acquired its first submarine, JS Kuroshio, in 1955.
She was the decommissioned Gato-class USS Mingo.
In 1956, Tokyo approved to build of an indigenous submarine, JS Oyashio. She was the only example
of its class and was commissioned in 1960. The Oyashio-class was followed by the Hayashio,
Natsushio, Ōshio, and Asashio classes, respectively. With the Uzushio-class, which was approved
in 1967, the JMSDF switched to teardrop design. The later Yūshio, Harushio, and Oyashio-classes
also had teardrop designs. The Sōryū-class is simply a modified version
of the Oyashio-class with air-independent propulsion, shortly AIP.
Actually, the JMSDF had been working on such a system since the late 1950s. But, all attempts
had been far from satisfactory. In 1986, the technology research department
of the JMSDF began to consider the Stirling engine.
The Swedish Kockums had been already testing the system since 1983.
After careful consideration, Japan decided to produce the Stirling AIP of Kockums and
modified the Harushio-class submarine JS Asashio with this system. The trials were conducted
in 2003. The result was successful. So, Tokyo approved the building of the Sōryū-class
submarines, which would be equipped with Stirling AIP, in the 2004 budget.
The first vessel of this class, JS Sōryū, was laid down in 2005, launched in 2007, and
commissioned in 2009. The complement of the Sōryū-class is 65-person.
The submarine has a length of 84 metres, a beam of 9.1 metres, and a draught of 8.5 metres.
Its surfaced displacement is 2,900 tons, while its submerged displacement is 4,200 tons.
The propulsion system consists of two 8,000 horsepower Kawasaki 12 V 25/25 SB-type diesel
engines and four 3,900 horsepower Kawasaki Kockums V4-275R Stirling engines. Its maximum
surfaced speed is 13 knots, while its maximum submerged speed is 20 knots. The Sōryū-class
can reach a range of 11,300 kilometres at a speed of 6.5 knots. The submarine has a
maximum diving depth of 650 metres. It has six 533mm torpedo tubes, and it can launch
the Type 89 torpedoes and UGM-84 Harpoon missiles. Japan built 12 Sōryū-class submarines.
But, the last two, JS Ōryū and JS Tōryū, do not have the Stirling AIP. There are no
dimensional changes between these two types. The teardrop hull design of the Sōryū-class
significantly reduces the hydrodynamic drag on the submarine when submerged. This hull
form provides better underwater performance. Also, low hydrodynamic drag means low noise.
So, the teardrop design allows the long side array sonar to be directly fixed to the pressure
hull while making the boat hard to be detected by sonars.
Yet, this hull form, which is patterned after the bodies of whales, decreases the sea-keeping
capabilities and increases drag while surfaced. Similar to the Oyashio-class, the entire hull
of the Sōryū-class is equipped with underwater sound absorbing and reflecting materials.
Also, its sail is tilted to reduce the target strength, which is a measure of the area of
a sonar target. The Sōryū-class completely reflects the incident sound in a direction
different from the sound source. Japan is one of the countries, which has invested
the underwater noise-reduction works the most. During an exercise in 1983, the JMSDF realized
that the latest detection systems on the P-3C Orions could easily detect the submarines,
even it stopped. This was a major shock to the submarine forces, and the reduction of
underwater noise became a top priority. As the result of these works, started in the
early 1980s, the Sōryū-class became one of the most silent submarines in the world.
As we mentioned before, the Sōryū-class has the same basic hull design as the Oyashio-class.
Yet, there are some important improvements. The Sōryū-class has an additional room for
the AIP, which is 11 meters long. Yet, the submarine is only 2 meters longer than its
predecessor. This reduces the volume of the living areas
and comfort. We can talk about the other differences.
For example, the curves of the bow and stern are changed, the sail is repositioned slightly
forward, and a streamlined cover called a fillet to the bottom is added.
The fillet also helps to reduce acoustic signature. The Sōryū-class has an X-shaped stern combination
of diving planes and rudders. The previous Japanese submarines had been equipped with
a cross-shaped rudder, which consisted of a vertical rudder for turning and a horizontal
rudder for depth control. Thanks to the new design, now all four control surfaces can
be used for both turning and depth control. This design provides superior manoeuvrability
to the Sōryū-class. Besides, in case one of the control surfaces is damaged, the other
three can control the manoeuvre horizontally and vertically.
The Stirling engine works based on the principle of expansion and contraction of gasses in
a variably closed volume. A reciprocating piston element displaces the gas in between
hot and cooled parts of the engine body, generating a sinusoidal power output on a second piston
element, which is coupled to the first one, to drive it as well as the output load.
JS Ōryū and JS Tōryū, which do not have the Stirling AIP, are the first submarines
in the world equipped with the lithium-ion battery. The development works on it as a
storage battery for the next generation of submarines began in 1987. Compared to conventional
lead-acid batteries, lithium-ion batteries do not have the danger of hydrogen gas generation.
Also, they provide more than twice the energy density per weight volume and 1.5 times more
times of repeated charging and discharging. Their charging time is shorter.
Yet, some sources claim that compared to the Stirling AIP-equipped variant, the last two
boats' shaft horsepower has decreased to 5,600 from 8,000.
The Sōryū-class is equipped with the CM010 optronics mast, which does not require a periscope
tube. Thus, it freed design space during construction and limiting risks of water leakage in the
event of damage. The optronics mast, also known as photonics mast, do not need to be
located directly above its user, and it requires only a small pressure hull penetration for
cabling. The main sensors and weapons of the Sōryū-class
are connected by a LAN. So, crew members can share more data quickly, and the common operational
picture can be generated immediately. The main armament of the Sōryū-class is
the 533mm active/passive acoustic homing Type 89 torpedoes. This wire-guided torpedo can
reach a range of 50 kilometres at a speed of 40 knots or 39 kilometres at a speed of
55 knots. Its maximum effective depth is 900 metres. The Type 89 has a 267-kilogram warhead.
Now, Japan is working on the new 533mm Type 18 torpedo. Different from the Type 89, it
has an acoustic image sensor that can identify the shape of the target and distinguish it
from the decoys. The torpedo is equipped with an active magnetic proximity fuse that is
also effective for decoy identification. It is also highly effective in coastal and shallow
waters. Japan expected to get its first Type 18s this year.
The UGM-84 is the submarine-launched variant of the Harpoon. This missile, whose range
is 124 kilometres, has a 222-kilogram semi armour-piercing warhead. Its maximum speed
is Mach 0.86. All Sōryū-class submarines are deployed
on the Kure and Yokosuka bases, which are faced to the Pacific Ocean. The location of
these bases protects them from an unexpected raid.
But, they have to go long distances before they patrol on the near seas of China, North
Korea, and Russia. Actually, the JMSDF generally deploys its
Sōryū-class submarines in the oceans rather than close waters.
It seems that monitoring and protecting the western seas are the job for the big surface
fleet and land-based aircraft squadrons of Japan.
Also, at first glance, we may say that the JMSDF does not intend to use its submarines
for intelligence-gathering missions. But, these observations may be misleading.
You know the phrase; there is no perfect crime. But, there is a strong counter-argument against
it. We can know only crimes, they are not perfect.
Until today, neither Japan nor other countries have mentioned the existence of a Sōryū-class
submarine, patrolling near China, Korea, or Russia.
Have they never patrolled, or have they never detected?
Let's leave the speculation here. The Sōryū-class submarines have shown themselves
at the far seas. JS Sōryū participated in the Malabar 2018
naval exercise, jointly conducted by the USA and India. But, she was not in the Indian
Ocean rather than the Pacific Ocean. JS Hakuryū conducted joined training exercises
near Sydney with the Royal Australian Navy. Most of these submarines participated in exercises
near Guam and Hawai. On October 9, 2020, alongside JS Kaga and
JS Ikazuchi destroyers, JS Shōryū conducted anti-submarine warfare training in the South
China Sea. One day later, she visited Vietnam for refuelling.
Considering its unique and innovative features, the Sōryū-class is one of the best diesel-electric
attack submarines in the world. It is undoubtedly a game-changer in the region. Yet, the submarine
has not achieved any commercial success in the international market although it was a
strong candidate for Australia and India. But, the main reasons for these failures are
not related to the submarine. As we mentioned in our P-1 video, there is
a psychological barrier to acquire Japanese systems.
No one wants to be first. To avoid repeating ourselves, we would not mention this and other
factors again in this video. Yet, we must add that while Japan wants to
achieve success in the international market with this submarine, it also has reservations
about sharing the advanced technologies it has developed, which were achieved after years
of hard work and big expenses. Also, now, Japan began to build a more advanced
Taigei-class. These submarines will replace the Oyashio-class.
Maybe Japan would sell the retired Oyashios first to create a market.
Sweden did it before. Many countries in the region, like the Philippines
and Taiwan, would be keen to accept such a deal.
So, it seems to be the Sōryū-class will be used by only the JMSDF for a while. Most
probably, we will not see the capabilities of this submarine in real combat, like many
other state-of-art Japanese weapon systems. If we accept that the real success of a weapon
system is deterrence, we should acknowledge that the Sōryū-class submarines do their
job perfectly. Thanks for watching our video. And please
don't forget to subscribe to our channel and give us a thumbs up if you liked our video.
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