Could LIBs be combined with Stirling AIP? - Table.

Anonymous has kindly provided the comments (original words) and further translated by Pete below on November 8, 2018.

A full Lithium-ion Battery (LIB) system was adopted on the first Japanese Soryu Mark 2 submarine ("SS" sequence number 27SS – see red in Table below), which was launched on October 4, 2018. [Pete comment: A LIB system not only means 100s of tonnes of new type batteries but new or altered electrical wiring, connections, adjusted propulsion motor, adjusted consumer hotel load equipment (eg. computers), and many other weight conscious rearranegements = new buoyancy settings.]

LIBs replace the Stirling air independent propulsion (AIP) and lead-acid batteries (LABs) in previous Soryus (see Table below). The Japanese Ministry of Defense (MoD) and Navy adopted LIBs, because they perceived major problems in Japan's 13 years of using Stirling AIP.

More specifically in the older Soryu Mark 1 (AIP + LABs) submarines Stirling AIP’s drawbacks probably include/included:

i)  major weight, balance-buoyancy changes as 10s of tonnes of liquid oxygen (LOx) is consumed in the heavy LOx tanks. See “Combat Technology of Submarine” 2015 by H. Yamaichi. Ex-captain of JS Setoshio (SS-575) which was a Yushio class submarine). He was is also ex-Professor in the National Defense Academy of Japan. He said “Weight of goods (water, food, etc) is strictly controlled in submarine.”

ii)  low AIP energy output, which effects acceleration and speed, 

iii)  Stirling AIP can only operate at a diving depth down to 200m. See more below on this last diving depth point.

iv) [Pete comment: Time needed to warm up the AIP? AIP cannot be instantly accelerated or switched on to confront a crisis, like a Chinese torpedo.] 

The relative high costs of LIBs and Stirling AIP is an uncertain issue. It is not known why Japan did not decide to retain Stirling AIP and then add LIBs in a new submarine. 

[Pete comment - Note that Japan’s needs submarine stored energy (be it diesel, battery electricity or AIP chemicals) that is appropriate to Japan’s mission requirements. Requirements which may vary from short defensive missions to longer (4,000+ km) range missions in the western Pacific. AIP very well meets requirements in small enclosed seas but can have major overall drawbacks in open seas/oceans.]

Further to point iii) above - by recharging in gentle seas the LIBs Soryu Mark 2s can be operate for a far longer period than LABs-AIP Soryu Mark 1s (whose fully submerged operational period is controlled by the limited amount of LOx carried in Mark 1s).

According to Japan’s MoD, the replacement of Stirling AIP-LABs is because LIBs allow a longer time submerged. “In simple thinking, this statement seems to be false because energy from Stirling AIP is nearly 100 MWh larger than that from LIBs” (50 MWh). But, if a Stirling AIP-LABs Soryu needs to operate below a depth of 200m, it can no longer utilise AIP [due to AIP's no greater than 20 bars exhaust pressure limitations] and instead must rely on its LABs.

AIP’s diving depth limited down to 200m is a problem because Japanese submarines are operated in the Sea of Japan and West Pacific Ocean which are much deeper than 200m. In those standard situation a LIBs Soryu will yield a longer submerge period than AIP-LABs Soryu. [Pete Comment: Note, in using AIP Soryu Commanders, do not want to forego their sub's unusually deep max diving depth - maybe around 700m.] 

So Japan’s MoD has selected LIBs Soryus for full range-operation deeper diving efficiency.

AIP More Useful for Some Other Navies

In the case of the latest Chinese Yuan class 039A/041 submarines which use [covertly acquired, indigenous and/or bought] Stirling AIP and LABs, the situation seems to be a bit different form Japanese submarines. These Chinese submarines are intended to be mainly operated in the East China Sea [and use this inter-active sea depth map] which is mostly very shallow (almost three-fourths of the sea is less than 200m). There, China’s Stirling AIP-LABs system is still effective.

For the same reason, Sweden’s SAAB Gotlands and future A26s are/will be effective in the mostly shallow Baltic Sea. [Pete Comment: Also missions in the Baltic can be very short so Swedish sub’s can completely use their AIP with no LABs needed. Singapore which is using Stirling and soon German AIP on the new Type 218s may also enjoy only-need-AIP operations.]

Sweden and other countries may be interested in AIP + LIBs. Stirling AIP seems to compatible with LIBs. LIBs are used for operation under depths of 200m, and Stirling AIP improves endurance in shallow water. 

Also the recovered heat from the combustion gases of Stirling engines can be used for heating of LIBs to avoid thermal runaway at low temperatures. Cold sea (eg. North Sea and Baltic) users benefit most from the recovery-heat differential nature of AIP. Potential users include  the Netherlands' Walrus Replacement, German, Norwegian Type 212A/CD and, of course Swedish A26s.  

Though France’s Naval Group and German TKMS have already reported interest and some development of LIBs for submarine (probably most in collaboration with SAFT) Sweden’s SAAB, has not said much about adopting LIBs.

TABLE for SORYU & Oyashio Program as at November 9, 2018 

SS No. Diesel Type Motor	Build No Name	Pennant No.	MoF approved amount ¥ Billions FY	LABs, LIBs, AIP	Laid Down	Laun -ched	Commi ssioned	Built By
5SS Oyashio 2 Toshiba motors	8105 Oyashio	SS-590/ TS3608	¥52.2B FY1993	LABs only	Jan 1994	Oct 1996	Mar 1998	KHI
6SS-15SS Oyashios  10 subs 2 Toshiba motors SMC-7?	8106 -8115 various	SS-591-600	¥52.2B per sub FY1994-FY2003	LABs only	15SS Feb 2004	15SS Nov 2006	15SS Mar 2008	MHI & KHI
16SS Soryu Mk 1 12V25/25SB SMC-8	8116 Sōryū	SS-501	¥60B FY2004	LABs + AIP	Mar 2005	Dec 2007	Mar 2009	MHI
17SS	8117 Unryū	SS-502	¥58.7B FY2005	LABs + AIP	Mar 2006	Oct 2008	Mar 2010	KHI
18SS	8118 Hakuryū	SS-503	¥56.2 FY2006	LABs + AIP	Feb 2007	Oct 2009	Mar 2011	MHI
19SS	8119 Kenryū	SS-504	¥53B FY2007	LABs + AIP	Mar 2008	Nov 2010	Mar 2012	KHI
20SS	8120 Zuiryū	SS-505	¥51B FY2008	LABs + AIP	Mar 2009	Oct 2011	Mar 2013	MHI
No 21SS			No 21SS built
22SS	8121 Kokuryū	SS-506	¥52.8B FY2010	LABs + AIP	Jan 2011	Oct 2013	Mar 2015	KHI
23SS	8122 Jinryu	SS-507	¥54.6B FY2011	LABs + AIP	Feb 2012	Oct 2014	7 Mar 2016	MHI
24SS	8123 Sekiryū	SS-508	¥54.7B FY2012	LABs + AIP	15 Mar 2013	2 Nov 2015	13 Mar 2017	KHI
25SS	8124 Seiryū	SS-509	¥53.1B FY2013	LABs + AIP	22 Oct 2013	12 Oct   2016	12 Mar 2018	MHI
26SS end of SMC-8s	8125 Shoryū	SS-510	¥51.7B FY2014	LABs + AIP	2014	6 Nov 2017	Mar 2019?	KHI
27SS First Soryu Mark 2 12V25/25SB  diesel first SMC-8B motor	8126 Oryū	SS-511	¥64.4B FY2015	LIBs only (NCA type)	2015	4 Oct 2018	Mar 2020?	MHI
28SS  Second Soryu Mark 2 12V25/25SB SMC-8B	8127	SS-512	¥63.6B FY2016	LIBs only (NCA type?)	2016?	Oct 2019?	Mar 2021?	KHI
29SS First Soryu Mark 3 12V25/31S SMC-9?	8128	?	¥76B FY2017	LIBs only?	?	?	2023?	MHI?
30SS Second Soryu Mk 3 12V25/31S	8029?	?	¥71.5B FY2018	LIBs only?	?	?	2024?	KHI?

Table from information exclusively provided to Submarine Matters. LABs = lead-acid batteries, AIP = air independent propulsion, LIBs = Lithium-ion Batteries. ¥***B = Billion Yen. MHI = Mitsubishi Heavy Industries, KHI = Kawasaki Shipbuilding Corporation of Kawasaki Heavy Industries. 

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Thankyou Anonymous (with further translation and some [bracketed] comments by Pete).