Japanese Navy Commissions JS Toryu (the last Soryu)

Words from Ryan White and experts on Japanese submarines, wispywood2344 and Anonymous, are on the Japanese Navy no longer building Soryu Mk.1s, commissioning the Soryu Mk.2s (JS Oryu and Toryu - the last Soryus) and bulding the follow-on Taigei-class.

The following is a summary of Ryan White's UK based Naval Post, on March 24, 2021, report:

"Japan commissions JS Toryu, its Second Submarine Running on Li-Ion Batteries"

The Japanese Navy commissioned its 12th and final Soryu-class sub, JS Toryu, at KHI's Kobe shipyard on March 24, 2021. Toryu is assigned to the 2nd Submarine Flotilla, Kure naval base. Like the preceding Soryu-class sub JSS Oryu, Toryu use LIBs from GS Yuasa with no Stirling AIP. The LIBs are lithium nickel cobalt aluminum oxide (NCA). LIBs require less maintenance, have longer endurance or permit higher speed compared to LABs. [See "Key to" the  SORYU Table in the article above for expansions of all these acronyms.]

[Pete Comment: Soryu subs are budgeted by the Japanese Finance Ministry in Japanese Yen and may average the equivalent of US$550 million for the longterm and only customer, the Japanese Navy. Export prices would be much higher with the need for risk, technology transfer and profit margins. JS Toryu itself cost around US$584 million, probably due to the extra development and production costs of its LIBs.].

Specs for the Soryu include: 84m long, 9.1m beam, 2,900 tonnes (surfaced), 4,200 tonnes (submerged), 65 crew. Max range 6,100nm at 6.5kn. 2 x 12V25/25SB Kawasaki diesels.

6 x 533mm torpedo tubes for Type 89 torpedoes, UGM-84 Harpoon AShMs and mines.
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Note: Naval Post is a UK based online defence media company, focused on Warships, Submarines, Naval Air, Marines, Coast Guard, and Naval Missiles. It started in 2016 with the name of “Naval News”. In 2021 it changed its name to Naval Post.
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On March 28, 2021 wispywood2344 (very knowledgable about Japanese submarines) provided a link and comments: which suggests:

Toryu's sonar system "ZQQ-7E" has progressed from Oryu's "ZQQ-7D-2" in the following ways;

A) Improved acoustic signal processing algorithms

B) Improved mechanical strength [level of breaking strain] of the TASS [= Towed Array Sonar System ]

The latter is worthy of note, because it strongly suggests an increase in patrol speed.

wispwood2344 concludes that one of the reasons why the Japanese Navy ("JMSDF") abandoned AIP and LABs and then adopted LIBs may be to expand the hourly patrol area by increasing the patrol speed.

AIP on Soryu Mk.1s allows 14 days continuous diving at inadequate speeds of 4kt or less. 

The fact that increased patrol speed is one of the development goals of the sonar system currently under development reinforces the speculation in this Japanese Ministry of Defense (MoD) link "Reiwa02 administrative review ; Development of the future submarine sonar system. " 

Pete has translated parts of it: "The submarine [Toryu] is scheduled to operate for about 24 years in the future, and during that period, it will collect information and monitor over a wide area while maintaining its superiority in the underwater area. In order to implement this, we will develop a sonar device that improves the detection capability and ensures the ease of capacity improvement in response to the improvement in patrol speed by towing....We will carry out detailed design and trial production of the mold array, a part of the signal processing unit and each component of the evaluation processing unit. In addition, to conductingg technical tests we will conduct practical tests over the fiscal year to verify the results."

This supports wispwood2344's conclusions.
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Anonymous (expert on Japanese submarines) on March 29, 2021 commented, to the effect:

As Stirling AIP generates-expels carbon dioxide into the surrounding seawater, the efficiency of AIP becomes 0% at 20 atmospheric pressure (= 200m dive depth). So, Stirling AIP must operate at much shallower depths - this might be an irritating situation which may become serious if a Soryu Mk. 1 wanted to dive (most quietly, using AIP) below 200m to avoid a threat. 

Anonymous has also advised in the past that the large liquid oxygen (LOx) tank that formed part of Soryu Mk. 1's AIP system was a heavy weight (even when exmty) to carry throughout a mission and then a declining-variable weight as LOx was consumed with AIP use (all leading to buoyancy problems-complexity). 

Stirling AIP's depth limitation, and buoyancy problems of AIP subs that rely on heavy-weight LOx, are some reasons for the removal of Stirling AIP from the Soryu Mk.1s.