April 1, 2022: In early March Japan put Taigei, the first (of seven) Taigei class submarines, into service. This came 18 months after Taigei was launched (put into the water) so that installation of equipment could be completed and sea trials conducted. All seven subs of this class are supposed to be in service by 2026. Each one will cost about $700 million.

These are successors to twelve Soryu class subs. The last two Soryus made the Taigeis possible. These two Soryus were called “Super Soryu” because of their new lithium-ion battery tech and the higher cost that went with this new feature. The two Super Soryus entered service in 2020 and 2021 and their success confirmed the design of the Taigei was sound. The Super Soryu were different from the other Soryus because they had a number of improvements, especially the lithium-ion batteries. The Taigeis are basically similar to the Super Soryus with a few additional enhancements. The Taigeis are 3,000-ton subs with a crew of 70, six torpedo tubes and a top speed of 37 kilometers an hour (submerged) and 24 kilometers an hour on the surface.

Several nations, including South Korea, China, Germany and the United States have been working on making lithium-ion battery technology work in subs and those efforts became particularly intense after 2015. The main obstacle was the safety of lithium-ion batteries in a submarine. Lithium-ion batteries are known to be dangerous under certain conditions. Consumer products like cell phones and laptops have had problems. Not a lot but enough of the hundreds of millions of cellphones and laptops using lithium batteries have burst into flames or exploded to make the general public aware of the risk. These overheating problems had to be minimized to levels that made lithium-ion batteries safer than the current lead-acid batteries used for over a century in submarines. Several nations believe they have achieved the needed safety levels and Japan was the first to put a lithium-ion boat into service. This is encouraging for China, South Korea and Germany, who are planning on building subs with this new battery tech. Now there are three such subs in service and there will be at least nine by 2028.

South Korea has started construction of a sub using lithium-ion batteries and it is supposed to enter service in 2026. This is the first of six Batch II subs of the Changho class. Only one of the three Batch I subs is in service but the second one enters service this year and the third one by 2024. The Changhos are about 15 percent larger than the Taigeis and cost about fifteen percent more.

Germany has developed its own lithium-ion batteries for subs and plans to use them in new subs as well as replacing lead-acid batteries in current German built subs.

China may already have one new sub equipped with lithium-ion batteries. China often tries to keep new developments like this secret for as long as it can.

The advantages of lithium-ion batteries are many. First, they store twice as much power as equivalent (in size and weight) lead-acid batteries. Lithium-ion batteries can release more power than lead-acid and take less time to recharge. Lithium-ion batteries do not degrade over time and have more recharging cycles. Lithium-ion batteries can enable subs to move faster under battery power. Putting out low levels (for low speed) of power, lithium-ion batteries can provide almost as much submerged time as current AIP (Air Independent Power) systems.

The last two Soryu class subs are dispensing with the AIP systems they were designed to use and rely only on lithium-ion batteries to provide the underwater endurance similar to that provided by AIP. This approach is also being watched closely by submarine builders because adding AIP is more expensive than installing lithium-ion batteries. The key factor is the safe operation of submarine lithium-ion batteries under all conditions, including accidents that damage the hull and internal equipment. This is something you can’t really test, only design for. The Japanese lithium-ion battery manufacturer insists they have all this covered. China was apparently convinced because they have built a few AIP subs but then said AIP was not worth the additional cost.

The quantity and quality of its submarines is important for Japan. Since the 1970s, Japan has maintained a fleet of at least 18 diesel-electric submarines. A decade ago, in the face of growing Chinese naval power, it was decided to increase the submarine force to 21 or 24 boats. Currently, there are 22 subs in service; one Taigei class, 12 Soryu class and 9 Oyashio class. There are another two Oyashios used training boats that produce sailors qualified to serve in submarine crews.

Since 1980 Japan has replaced their subs after about 25 years, with newer designs based on experience with the previous classes. The current expansion was accomplished by building more of the new Soryu class. A decade ago, there were two Soryu class boats in service and four under construction. These 2,900-ton boats have a crew of 65, six 533mm (21 inch) torpedo tubes and 30 torpedoes or Harpoon anti-ship missiles. There are also two 76mm tubes for launching acoustic countermeasures. Sonar and electronics are superior to the previous class. These boats also have AIP that enables them to remain submerged for a week or more at a time. These subs cost about $665 million each.

Currently, Japan also has eleven 2,700 ton Oyashio class subs, built 1994-2008. With a crew of 70, they are armed with six 533mm (21 inch) torpedo tubes and 27 torpedoes or Harpoon anti-ship missiles. Their sonar equipment is superior to that of the previous Harushio class. Top surface speed is 24 kilometers an hour, top submerged speed is 37 kilometers an hour.

Japan has retired its seven Harushio class boats, including two diverted to training duties. These 2,400-ton boats were built 1987-1997 and have crews of 65-70 sailors. They are armed with six 533mm (21 inch) torpedo tubes and 26 torpedoes or Harpoon anti-ship missiles. They have hull-mounted and towed sonar. Top surface speed is 24 kilometers an hour, top submerged speed is 37 kilometers an hour.

China currently has about 58 submarines, none of them as effective as the Japanese boats, despite eight of them being nuclear. The Japanese crews are also better trained, but the Chinese are building better ships with more intensively trained crews. Two other Chinese neighbors, South Korea and Australia are also increasing their submarine forces.