The U.S. Navy and Japan Maritime Self-Defense Force (JMSDF) are known for close (and closely held) submarine operational coordination. That said, the JMSDF’s successful mounting of lithium-ion batteries in the Taigei, its new diesel-electric submarine, is a significant technical breakthrough that should be the subject of both a technology and an operational exchange between the United States and Japan. It is an opportunity to examine the use of naval high-power batteries for both countries. The Taigei not only has significant technical ramifications, but also raises pivotal operational factors with strategic-level implications.
Technically, the U.S. Navy would do well to review the analytical approach taken by the JMSDF toward battery chemistry before it decided to replace its air independent propulsion (AIP) and lead acid battery propulsion plant. In total, the JMSDF reviewed ten lithium-ion options before narrowing them down to lithium nickel cobalt aluminum oxide (NCA) and lithium titanate (LTO). It compared the NCA chemistry’s higher voltage and battery capacity with LTO’s higher charge/discharge rate, significantly longer life cycle, and (now proven) inherently safe chemistry. Understanding the reasons the JMSDF chose NCA would help the United States in its own battery research.
The JMSDF released a tender to build the lithium-ion battery to two domestic suppliers: GS Yuasa and Toshiba Corporation. GS Yuasa, a large industrial lithium-ion battery producer, supports international customers in multiple sectors and is a significant sponsor of research and development related to lithium-ion battery densities. Having both public- and private-sector presence undoubtedly helps develop technical talent. Toshiba, one of Japan’s largest multinational conglomerates and top defense contractors, has provided electronics and other technologies for the country’s military for decades and has provided advanced lithium-ion propulsion batteries for the JMSDF’s new deep-submergence submarine rescue vehicle (DSRV). The multi-domain participation of its workforce supports talent across multiple technical sectors, and Toshiba’s battery business benefits greatly from its vertical integration. These firms’ research and development and industrial capacity and their relationship with the government of Japan should be of interest for U.S. planning.
Japan’s testing of lithium-ion batteries for mounting in the Taigei appears to have been rigorous and independent—conducted by the Defense Ministry’s Acquisition, Technology & Logistics Agency (ATLA). This arrangement and the process for testing and certification are potentially important points of interest for the navy-to-navy dialogue, especially given that Defense News reports that “Japan introduced lithium-ion batteries into its submarines after a lengthy development and testing period, which started as far back as 2002. Extensive testing starting in 2006.” This long-term focus and its context bear careful examination.
Given the instances of spontaneous combustion of some lithium-ion chemistries, U.S. analysts also should understand how the JMSDF addressed the safety implications of incorporating lithium-ion batteries at sea, in particular, in the closed environment of a submarine. Lingering concerns, including combustion caused by impurities introduced in the manufacturing process, are one reason strict production-line quality control is so important. These and other safety concerns, including hydrogen outgassing, have been mitigated or solved by physical design, battery controls, and advances in battery chemistry over the past decade.
A technical discussion would help the United States understand the JMSDF’s decision to pursue the Taigei solution rather than the AIP Stirling engine and lead acid batteries in the Sōryū class. Its calculations and experience with underwater speeds, endurance, and indiscretion rates achieving low signature and long submerge time would be illuminating. This is especially so given the reported $540 million price of the Sōryū versus the Taigei at $720 million, which underscores JMSDF confidence in lithium-ion propulsion.1 Apparently, the JMSDF concluded the higher cost was worth the wait to fit it into the budget. Also, it would be significant if JMSDF confidence in its Taigei solution clears the way for the more general use of lithium-ion batteries and their increasingly higher power.
Operationally, JMSDF tactical employment concepts for the Taigei are another important topic for discussion. This would include the advantages of eliminating the AIP set and its cycles, as well as being able to operate submerged at high speed and for longer periods at low speed.
Potential tactical advantages of lithium-ion batteries include the ability to discharge energy and recharge faster than other non-nuclear submarines. The fast discharge rate translates into more rapid dive times and the ability to move faster submerged, and the reduced indiscretion rate afforded by rapid recharging has considerable operational significance, including but not limited to fleet barrier operations amid the capes, headlands, straits, and archipelagos of the first island chain.
This is not to suggest that the U.S. Navy consider building diesel-electric submarines. That debate can continue elsewhere. However, the Taigei and related current technical and operational developments should call into question the U.S. nuclear Navy’s antipathy to battery propulsion, even if not in the context of its own force structure. First, this is an opportunity to reconsider the operational advantages that lithium-ion battery powered JMSDF submarines will bring to combined U.S. Navy–JMSDF fleet operations in and near the first island chain and on China’s maritime approaches.
Second, all navies are rapidly developing and integrating large fleets of battery-powered submersibles, the U.S. Navy included and notwithstanding its nuclear power preferences. These submersibles just happen to be unmanned. The proliferation of unmanned underwater vehicles will further drive renewed emphasis on lithium-ion propulsion derived advantages in submarine stealth and indiscretion rates.
Third, given the recent announcement regarding nuclear submarines for Australia, these and other U.S.–Japan operational considerations are even more salient and necessarily should include the Royal Australian and Royal Navies. One issue will be whether and how to reinforce current operational advantages and “flood the zone” with more diesel-electric and nuclear submarines.
The presumed spin-on technical and operational benefits of the Taigei class will be an important factor in submarine competition with China. An understanding by both navies of the Taigei’s technical specifications and tactical performance will add to allied interoperability and operational dominance.
1. James Holmes, “It’s Unlikely, But U.S. Diesel Subs Would Be One Way to Take on China,” War Is Boring, 18 March 2017; and “Japan Unveils New Submarine in Face of China’s Growing Assertiveness,” The Japan Times, 14 October 2020.
2. Mike Yeo, “Japan Commissions Its First Submarine Running on Lithium-ion Batteries,” Defense News, 6 March 2020.