On March 5, 2020, Japan’s first lithium battery submarine "Yinglong" held a delivery and flag-raising ceremony at Mitsubishi Heavy Industries Kobe Shipyard. The submarine was approved by the Ministry of Defense in 2015 in accordance with the "Medium-Term Defense Force Development Plan" (2014-2030). Construction began in November 2015 and it was launched in October 2018. After outfitting and several sea trials, it has been in service for 4 years and 4 months. Due to the COVID-19 pandemic, only personnel from the Ministry of Defense, the Self-Defense Forces, and the shipyard attended the ceremony. After the ceremony, the Yinglong left Kobe and was assigned to the 3rd Submarine Squadron of the 1st Submarine Squadron in Kure City, Hiroshima Prefecture on the same day.
’ Yinglong is the 11th ship of the Canglong class, but the boat has dismantled the Stirling engine and lead-acid batteries used by the previous Canglong class and replaced them with lithium-ion batteries (hereinafter referred to as lithium batteries). It is an improved version of the Canglong class with a replaced power unit, becoming the 20th submarine in the expansion of Japan’s submarine organization to 22 ships, and the world’s first submarine powered entirely by lithium batteries. The construction cost of the boat is about 64.3 billion yen (excluding advance funding, limited to the design fees and special equipment fees of specific national defense equipment, mainly referring to the costs invested in the initial stage of construction), which is more than 10 billion yen more than the construction cost of the 10th "Xianglong" approved for construction in 2014 (about 51.7 billion yen, with the mass production of this class of boats, the cost decreases from boat to boat), which may be related to the high-priced lithium batteries using rare metals. The "Doulong", which is also equipped with lithium batteries, was delivered on March 24, 2021, marking the last service of the Canglong class. It can be said that these two boats are lithium battery test boats of the Taijing class, which are of great significance in connecting the past and the future.
Main performance
Appearance
Because it is a quasi-same type of boat, the "Yinglong" has the same appearance as the Canglong class. The hull and the command platform are covered with anechoic tiles, which not only suppress and scatter the reflected sound waves of the active sonar, but also play a role in reducing the mechanical noise of the boat. In addition, fillets are installed at the connection between the front of the command platform enclosure and the hull to reduce fluid noise.
The stern is equipped with an X-shaped rudder, which provides good maneuverability for the submarine due to its high rudder efficiency. At the same time, the rudder surface does not exceed the hull outline, which can avoid damage to the rudder surface when the submarine lands on the bottom. So far, the "Yinglong" is no different from the Canglong class. The only difference is that the propeller at the rear of the X-shaped rudder is equipped with a new type of propeller different from the previous one to suppress the noise (mainly cavitation) within this speed range because the lithium battery can greatly improve the submarine’s ability to maintain medium and high speeds.
Structure
The pressure hull of the "Yinglong" is divided into 6 watertight compartments by the pressure bulkhead, from the bow to the stern, they are the 1st to 6th compartments. The first compartment is a two-layer structure, the upper layer is the torpedo compartment, and the lower layer is the crew living area. The second cabin is a three-layer structure. The upper floor is a combat command center that integrates boat operation and weapon control, and there is also the only single room on the boat: the captain’s room; the middle floor is the electronic equipment room and communication room, and the lower floor is equipped with a battery compartment. The third cabin is also a three-layer structure. The upper floor is the officer’s office and officer’s cabin, the middle floor has a restaurant, kitchen, cold storage room and crew cabin, and the lower floor is the battery compartment. In the fourth cabin, the relevant AIP equipment on the Canglong class is arranged in two layers, but the "Yinglong" has changed from two layers to three layers. The middle and lower floors are both battery compartments, and the upper floor is arranged with battery-related equipment, oxygen storage devices, etc. The fifth cabin is the main engine room, which is equipped with diesel engines, generators, auxiliary engines, etc. The sixth cabin at the rear is equipped with main propulsion motors, propulsion shaft brackets and other equipment, and the propulsion shaft directly connected to the main motor transmits power to the propeller.
Propulsion system
"Yinglong" is the world’s first submarine to use lithium batteries as the main power source. Therefore, if you don’t understand the characteristics of lithium batteries, you can’t grasp the characteristics of the submarine’s propulsion system. So, here we will use more words to introduce lithium batteries and propulsion systems. The 2019 Nobel Prize in Chemistry was awarded to three scientists who made outstanding contributions to the research and development of lithium batteries, one of whom was Japanese. In 1991, Japan took the lead in the practical application of lithium batteries. In 1994, Japan Battery Co., Ltd. (now GS Yuasa), which noticed the advantages of lithium batteries, proposed a research plan for lithium batteries for submarines. In order to meet the power supply of the entire boat during underwater diving, submarine lithium batteries need to have a super-large capacity far exceeding conventional batteries such as lead-acid batteries, and a large amount of energy must be stored in a confined space such as a submarine, which must be safe and reliable. From 1997 to 2004, the Technical Research Headquarters of the Japanese Defense Agency carried out four studies on "large capacity", "group battery", "battery management system" and "submarine adaptation technology", and finally realized the practical application of lithium batteries on submarines.
In short, lead-acid batteries obtain electrical energy through chemical reactions between the positive and negative electrodes and the electrolyte, while lithium batteries obtain electrical energy by simply moving lithium ions between the positive and negative electrodes in an organic electrolyte (without chemical reactions): during charging, lithium ions are released from the positive electrode and reach the negative electrode through the electrolyte; during discharging, lithium ions are precipitated from the negative electrode and reach the positive electrode through the electrolyte.
Lithium batteries are composed of metal foils to form positive and negative plates, on which thin film separators are added, and single cells are stacked alternately. Therefore, it can be made into a lightweight battery with a high energy density (the energy that can be released per unit mass or capacity) more than twice that of lead-acid batteries. Other advantages of lithium batteries include: high charging and discharging efficiency, long service life, and up to thousands of cycles due to the absence of chemical reactions; no gas or electrolyte volume changes caused by chemical reactions, good safety, and a sealed structure can be used for easy maintenance; no pollution, zero emissions, and good environmental protection; high output voltage of single cells, etc.
The first 10 Canglong-class ships use traditional lead-acid batteries and "Stirling" engines as source power. The hull is divided into 6 watertight compartments. The bottom of the 2nd and 3rd compartments are equipped with lead-acid batteries. The 4th compartment is the AIP equipment area. The upper floor is 4 60-kilowatt "Stirling" engines and related equipment, and the lower floor is equipped with 2 liquid oxygen tanks for liquid oxygen storage and supply. The "Yinglong" has removed all equipment related to lead-acid batteries and "Stirling" engines, and the vacated space is equipped with hundreds of lithium batteries and related equipment. In particular, the structure of the 4th compartment has been greatly changed to a 3-layer structure, with lithium batteries arranged in the lower 2 layers. In this way, the battery compartments of the "Yinglong" were increased from the 2nd and 3rd compartments of the original Canglong class to the 2nd, 3rd and 4th compartments. Due to the difference in voltage between lead-acid batteries and lithium batteries and the expansion of capacity, the "Yinglong" redesigned the submarine’s battery circuit and its protection device on the basis of ensuring propulsion. In addition, along with the abandonment of lead-acid batteries, the supporting battery water cooling and electrolyte stirring equipment were replaced with auxiliary equipment such as air cooling synchronized with lithium batteries. Through this modification, the "Yinglong" ensured underwater maneuverability similar to that of the Canglong class.
Because lithium batteries can confirm the accurate power capacity through the battery voltage, and the self-discharge rate is about 1% per month, it is not easy to produce deviations between each group of batteries. It can be said that they are basically maintenance-free batteries. However, due to the extremely high energy density, it is necessary to always confirm that the battery is in a safe state when stored in a narrow and confined space, especially the management of charge and discharge and temperature is particularly important. Therefore, the "Yinglong" is equipped with a new battery management and alarm system, which monitors the voltage, current, temperature and other parameters of each battery group at all times, and will immediately alarm once the set threshold is exceeded. Moreover, sufficient margin is left for the threshold of the alarm point to ensure safety.
As mentioned earlier, lead-acid batteries obtain electrical energy through chemical reactions. The disadvantage is that during high discharge, there will be a time delay in the homogenization of the electrolyte, the battery voltage drops sharply, and the battery capacity decreases. Lithium batteries only extract electrical energy by ion movement. During high discharge, the battery voltage decreases slowly, and the phenomenon of battery capacity reduction is not obvious. They can continuously discharge several times more than lead-acid batteries. Therefore, lithium batteries can provide high-power power to the propulsion motor for a long time, and the submarine’s underwater maneuverability at medium and high speeds is significantly improved.
Starting from the Canglong class, the conventional submarines of the Maritime Self-Defense Force will replace the main propulsion motors that are matched with lead-acid batteries with AC motors called "multi-rotor permanent magnet synchronous motors". Its main feature is that the rotor uses permanent magnets, which not only achieves small size and light weight, but also does not require carbon brushes and commutators, so it has a good noise suppression effect. In addition, there is no need for speed switching operation of DC motors, and it can change speed steplessly and smoothly. The "Yinglong" also uses permanent magnet motors, but in view of the characteristics of lithium-ion batteries, the main propulsion motor with this as the main power source should be a new permanent magnet AC motor that is suitable for continuous operation at medium and high speeds, rather than a permanent magnet motor that is matched with lead-acid batteries, otherwise it will be significantly restricted in use. According to the administrative business review table published by the Ministry of Defense, the main motor budget of the "Yinglong" is about twice that of the "Xianglong" in the previous year, which can be concluded that the boat uses a new permanent magnet motor. The motor is installed in the 6th cabin and drives the new propeller through the propulsion shaft, which improves the maneuverability of the "Yinglong".
In addition, lithium batteries also have excellent characteristics in terms of charging. Lead-acid batteries need to be charged at a voltage proportional to the battery temperature. If the voltage exceeds this, the electrolyte will be electrolyzed, accompanied by hydrogen generation and reduced charging efficiency. Therefore, the battery capacity can only reach about 80% when the engine power reaches full load. In contrast, lithium batteries do not react chemically when charged. When the engine is working at full load, the battery capacity can reach 95%, which can significantly shorten the charging time. As we all know, when charging, conventional boats need to get close to the water surface, extend the snorkel out of the water, start the diesel engine, and charge. When charging, the operation of the diesel engine will generate noise, and the snorkel and mast extending out of the sea surface are also easily detected by the enemy. Therefore, shortening the charging time has always been the unremitting pursuit of conventional boats.
In order to maximize the characteristics of lithium batteries, it is necessary to improve the performance of equipment such as diesel engines and generator snorkels. According to the technical research plan of the Ministry of Defense, the research and development of the "new snorkel power generation system" was carried out from 2010 to 2015. It is speculated that this is a project for lithium batteries, with the purpose of developing a higher-power diesel engine and a new snorkel device with higher efficiency. However, judging from the research time, even if the plan progresses smoothly, it is a bit reluctant to install it on the "Yinglong" which was only started to be built at the end of 2015. In addition, if new main engines, snorkels and other equipment are to be replaced, the hull must be significantly modified, which is a problem in terms of time. Therefore, the "Yinglong" should still use the two Kawasaki 12V25 diesel engines and auxiliary equipment such as snorkels of the Canglong class.
Because it is a quasi-same type of boat, the main performance of the propulsion system of the "Yinglong" has basically not changed. The biggest difference is that the shaft power of the "Yinglong" is lower.
Regarding the underwater speed, the "Yinglong" is equipped with a large-capacity lithium battery and the main circuit has been changed. Therefore, compared with the maximum power when the lead-acid battery capacity is 100% and all batteries are connected in series (in combat, it is almost instantaneous output power), the maximum power supply may be slightly lower, and the speed may barely reach 20 knots. However, given the characteristics of lithium batteries that can discharge at high power for a long time and that it is almost impossible to avoid torpedo attacks by maneuvering at a speed of only 20 knots, the slight reduction in its performance will not have a big impact.
Submarine control system
Submarine control system refers to the control system of the submarine’s weight, attitude, power and internal environment. The new system integrates all distributed functions such as operation and control beside each device in the past, and builds a system that can remotely control and monitor the working conditions of machinery and equipment in the combat command center. The system consists of two operation control consoles (MCC) including an X-shaped rudder operation control console and four boat condition control consoles (SCC). The MCC is installed on the front of the port side of the combat command center in the second compartment, and the SCC is installed on the port side. The two are arranged in an I-shaped pattern.
Living environment
The Soryu class has added a watertight compartment on the basis of the Oyashio class. Although many equipment such as the "Stirling" engine have been added, the length of the boat is only 2 meters longer. Therefore, the outfitting density in the boat is extremely high, and the living space is squeezed and very small. In addition, the officer cabin also adopts a large opening, and the overall living environment has regressed. On the contrary, the Oyashio class gives people the feeling that a lot of precious space is wasted.
In addition, with the installation of the AIP system in the Soryu class, the diving time is greatly extended. In order to ensure the physical and mental health of the crew, air management in the boat is one of the important measures. It is not only equipped with air monitoring devices to monitor the cleanliness of the air at all times, but also strengthens the carbon monoxide and carbon dioxide removal devices. The Yinglong has adopted these devices. As for oxygen, which is the most important for the survival of the crew, the oxygen in the oxygen storage tank of the Stirling engine can be partially used on the Canglong class, but the Yinglong has removed the Stirling engine and its ancillary equipment, so a small oxygen storage tank is installed in the fourth compartment to solve the oxygen supply problem.
Command and control system
The Yinglong has basically adopted the command and control system of the Canglong class. The system is responsible for the control of various sensors such as submarine sonar, periscope, electronic support measures, intelligence processing, target motion element analysis, and weapon system control. The system adopts an autonomous distributed architecture with the main signal transmission device as the core, and the main auxiliary system is connected to the fiber optic local area network. The system’s tactical situation display device is located in the central part of the rear of the combat command center, and 7 multi-function water-cooled universal display and control consoles (MFICC) are installed on the starboard side, which can manage all tactical intelligence in a unified manner.
Sonar system
Initially, the Maritime Self-Defense Force expected the "Yinglong" to be equipped with a towed array sonar and its signal processing equipment that increased the cable length and enhanced the detection capability. However, according to the administrative business review table published by the Ministry of Defense, the 12th Canglong-class boat "Doulong" approved for construction in 2016 was first equipped with the ZQQ-7E improved sonar system, and an advance allocation was made, so the "Yinglong" was not equipped with this sonar system, but the original ZQQ-7D Sonar system.
ZOO-7D sonar system is equipped with a "wet end" (underwater equipment of the sonar system) in the non-waterproof part outside the hull, a bow sonar is installed in the bow rubber fairing, side array sonars are installed on both sides, a towed linear array sonar and retractable equipment are installed at the stern, and a receiver for electronic support measures is installed on the upper part of the bow, which is roughly the same as the Soryu class. As a "dry end" (computers equipped in the boat, etc.), the boat is equipped with audio signal processing equipment, phase adjustment processing equipment, etc.
Torpedo launcher
There are 6 HU-606 533mm torpedo tubes in the torpedo compartment, arranged parallel to the centerline of the hull, 2 on the upper level and 4 on the lower level. This type of tube reduces the speed requirement for the submarine when launching torpedoes, which is conducive to improving the submarine’s combat capability at higher speeds. It can launch Type 89 torpedoes and "Harpoon" anti-ship missiles. In addition, the torpedo compartment is also equipped with a torpedo tube switch device, torpedo storage and automatic loading devices.
TCM launcher The Soryu class has been equipped with a torpedo countermeasures launcher since the 8th ship. The Yinglong is also equipped with a TCM launcher, which is located at the rear of the hull and can launch self-propelled decoys and torpedo jammers.
Conclusion
The Yinglong has expanded its maneuverability at medium and high speeds. Some people may question the cost-effectiveness of its underwater maneuverability, which is slightly higher than that of the Soryu class, but the cost is 10 billion yen higher. However, the advantages of lithium batteries are not limited to improving maneuverability. Its biggest advantage lies in the recovery of underwater maneuverability. As mentioned earlier, the Soryu class tried to use lead-acid batteries + Stirling engines to improve underwater maneuverability, but if the oxidizer (liquid oxygen) and fuel (kerosene) used by the Stirling engine are exhausted, it is necessary to return to the port for replenishment or resupply at sea. Lithium battery submarines can restore their maneuverability 100% almost unlimited times by simply charging in safe sea areas and harbors. Moreover, lithium batteries have high charging efficiency and can be charged urgently. The greater the engine power, the more this feature can be maximized. For conventional submarines, lithium batteries are a revolutionary equipment that can greatly improve the performance and combat deployment capabilities of submarines, and may also have an impact on the current submarine combat mode.
However, the "Yinglong" is a conventional submarine after all. The maximum output power of the battery is only 1/10 of that of the Ruby class, the nuclear submarine with the smallest tonnage and the lowest reactor power. The generated electricity must also be allocated to the weapon system and propulsion system. Improving the performance of the weapon system (especially the sonar system requires a lot of electricity to improve the detection capability) and increasing the number of weapons carried also require increasing the power distribution to the weapon system, which will affect the maneuverability. Moreover, even at medium and high speeds, the maneuverability and underwater combat capability of the "Yinglong" cannot be compared with nuclear submarines. Although the frequency of surfacing has been reduced, it cannot completely eliminate the snorkel state navigation.
Looking at the surrounding situation, North Korea is deploying a number of conventional submarines carrying ballistic missiles, which are highly maneuverable and concealed. Even with lithium battery submarines with greatly improved performance, it is difficult to respond effectively. Only nuclear submarines with excellent underwater maneuverability and strong detection and attack capabilities can complete this task. In addition, China’s submarine force is one of the top underwater forces in East Asia and even in the world. In recent years, it has also been updated and replaced on a large scale; South Korea is also carrying out a nuclear submarine development plan and trying to own nuclear submarines. In view of this situation, Japan wants to thoroughly strengthen its underwater defense capabilities, and owning nuclear submarines is an inevitable choice.
