The 29SS, just like 16SS Soryu before it, and KSS-III as well, is not a monolithic submarine design. This submarine will last a generation and it's inevitable that some of its later-batch ships will incorporate new technologies that were not applied on earlier vessels of the same class. The larger Japanese submarine was in the works for the target date of Heisei 28~29 (2016 is Heisei 28). The 28SS was pushed back to 29SS due to Japan missing a submarine (SS-506) for lay-down in 2010 due to recession. That delayed the 28SS program (SS-513) by 6 months for launch in May 2020, rather than October/November 2019 as originally planned.
Japan's next line of submarines feature extended hull and redesigned positioning of fuel tanks compared to Soryu. Japan decided to go hybrid AIP + Li-Ion for their future subs. The Fuel cell + LiBat hybrid technology of 29SS ensures that the enlarged Soryu NG (a semi-predecessor of 29SS for RAN needs) has more range than either Collins Evolved or any of its competitor.
The US Pacific Command said that Japan's future boats are going all Li-Ion, including the 29SS, not hybrid AIP + Li-Ion. According to PACOM, the Japanese approach is to fill the space available from removing the AIP system with more Lithium-Ion batteries: The Japanese Ambassador to Australia, Sumio Kusaka, seems to confirm this in his public pitch for the Soryu, which was written in April 2016: "Japan has experience operating seven submarines installed with AIP systems. But after considering the evolution in lithium-ion battery technology—higher energy density, greater safety, faster recharging times—Japan decided not to install AIP systems on submarines that will be built from 2015 onwards."
Japan decided to power its new batch of Soryu-class submarines with Lithium-ion batteries instead of air-independent propulsion (AIP) technology — a move that could raise eyebrows after similar types batteries were faulted for fires aboard the Boeing 787 Dreamliner. However, experts brushed aside those concerns and instead say this type of technological leap increases power and performance, while reducing maintenance. It also could make Japanese subs more marketable overseas. Yasushi Kojima, a spokesman for the Maritime Self-Defense Force (MSDF), said in October 2014 that the change would affect the next four remaining Soryu-class submarines in Japan’s 10-boat class. By shifting to Lithium-ion batteries, the new Soryus would retain their main propulsion diesels, but be equipped with more powerful and far lower maintenance batteries than lead-acid types widely in use.
Metal hydride fuel cells are a subclass of alkaline fuel cells that are in the research and development phase. A notable feature is their ability to chemically bond and store hydrogen within the cell. This feature is shared with direct borohydride fuel cells, although the two differ in that MHFCs are refueled with pure hydrogen. Though the absorption characteristic of metal hydrides (around 2%) is far lower than sodium-borohydrides and other "light" metal hydrides (around 10.8%), prototypes have been claimed to demonstrate a number of interesting characteristics. Metal hydrides fuel cells are being researched by ECD Ovonics, as well as by the Japanese National Institute of Advanced Industrial Science and Technology (AIST). Though similar, the two MHFC concepts use different catalysts.
In April 2016 some technical information on the modified Soryu-class submarine proposed by Japan for Australia's AUD50 billion (US$37 billion) Future Submarine program were disclosed for the first time to correct what the Japanese embassy described as erroneous information related to the Soryu's specifications and capabilities. The details were included in an unusual statement sent by Japanese ambassador Sumio Kusaka to the Australian Strategic Policy Institute (ASPI) and to specialist media. According to the statement, concerns that the Soryu would not be able to meet the Australian cruising range requirements were unfounded; the fuel load would be increased by extending the hull and re-designing the positioning of fuel tanks.
Taigei, the new submarine for the Japanese navy, was launched 14 October 2020 from a Kobe shipyard as part of the country's maritime security enhancement strategy amid increasing aggressiveness by China in the region. The 3,000-ton ship was built by Mitsubishi Heavy Industries and is due to enter service in March 2022. It is the 22nd unit of the Japanese Maritime Self-Defense Forces submarine fleet.
Taigei, which means large whale in Japanese, is 84 meters long and 9.1 meters wide. It carries 70 crew members, has a stealth design and is equipped with lithium-ion batteries that allow it to be underwater longer than previous models. It was built at a cost of 76 billion yen (US $ 720 million).
The Taigei will be the first in the new Taigei-class category, following the Oyashio and Soryu classes.In 2010, Japan set out to increase the number of submarines from 16 to 22 as China's increased activities in waters near Japan, especially around a group of islands administered by Japan and claimed by Beijing. Japan currently operates nine 2,750-ton Oyashio-class submarines and 11 of the 2,950-ton Soryu-class warships, and is planning to receive a new 2,950-ton Soryu-class submarine that will bring its fleet to 23.
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