The Dawn of a New Age in Naval Submarine Propulsion

On Thursday 5th March 2020 the Japanese Maritime Self-Defense Force (JMSDF) commissioned the 11th Soryu-class diesel-electric attack submarine (SSK), the JS Oryu (SS-511). The JS Oryu is the world’s first operational naval attack submarine to be equipped with lithium-ion (LIB) main batteries, replacing the lead acid (LAB) main batteries and air independent propulsion (AIP) systems fitted to earlier Soryu-class submarines.

A second Soryu-class submarine equipped with LIB main batteries, the JS Toryu, was launched in November 2019 and is expected to enter service in March 2021.

There is very little published technical detail about the JS Oryu’s LIB main batteries, but it is understood that they have approximately double the capacity of the earlier Soryu-class LAB main batteries. This would give JS Oryu about twice the submerged patrol endurance (battery-only), and around three times the endurance when running submerged at full speed.

Notwithstanding the lack of technical detail, a number of conclusions can reasonably be drawn from the commissioning of JS Oryu on schedule, and the launching of JS Toryu in November 2019 (also on schedule).

It’s reasonable to assume that the JMSDF required the JS Oryu to meet stringent operational performance and safety requirements during its commissioning trials, and that any significant problems experienced with the LIB main battery system would have resulted in delays for rectification and/or redesign.

The performance trials would likely have included:
  • extended snort charging at or above normal operational requirements
  • submerged low speed patrol and high speed running to the limits of the LIB main battery performance and endurance
  • charging and discharging of the LIB main battery system at its maximum specified rates
  • charging of the LIB main battery system to 100% State-Of-Charge (SOC)
  • rigorous testing and evaluation of control, monitoring and safety systems for the LIB main battery system
It’s also reasonable to assume that any significant redesign of the LIB main battery system would have led to protracted delays for both the commissioning of JS Oryu and the launching of JS Toryu. Following the launching of JS Oryu in October 2018, there has been no published information to suggest that any significant issues were encountered with the LIB main battery system during the trial period.

JS Oryu and JS Toryu will provide valuable operational data and experience to assist the development of the Soryu class successor, the 29SS class. The 29SS class submarines will also be equipped with LIB main batteries, and are expected to enter service in the early 2030s following an extensive period of research and development in the mid-late 2020s.

The doubling of main battery capacity for JS Oryu and JS Toryu is the most significant proportional increase in the main battery capacity of conventional naval submarines since Germany introduced the Type XXI Electroboat towards the end of WW2.

The Type XXI tripled the main battery capacity of previous U-boats, and this enabled the transition from submersible to submerged submarine design and operation. However, following the introduction of the Type XXI there was no significant improvement in the capacity of LAB technology, and the basic parameters of conventional naval submarine performance and operations remained largely unchanged until the introduction of AIP technology into operational service in the 1990s.

By comparison, the gravimetric and volumetric energy density of LIB technology has been doubling every decade since the early 2000s, and this trend is expected to continue for the foreseeable future as both LIB and future advanced light metal battery (LMB) technologies continue to evolve, driven by historically high levels of global investment in research and development and scale of production, and the accelerating global adoption of LIB technology across all transport sectors and large scale electricity grid stabilisation.

The designers of the first generation of LIB-equipped naval submarines (Japan and South Korea) have adopted a conservative approach, ensuring that they will operate within generous operational safety parameters while valuable operational knowledge and experience is acquired to inform the design of more advanced second generation LIB-equipped submarines that will enter service in the 2030s and 2040s.

By the late 2030s/early 2040s it is now reasonable to expect that LIB-equipped submarines will have main battery capacities 4-5 times larger than their LAB-equipped predecessors. This will bring significant advantages for zero-indiscretion submerged patrol endurance, faster transit speeds, extended high speed submerged running, stealthy operation and advanced energy-intensive combat systems.

LIB-equipped submarines entering service in the mid-late 2040s will have main battery capacities measured in hundreds of megawatt-hours (MWh) compared to the tens of megawatt-hours of LAB-equipped submarines (the Collins LAB main battery has a nominal capacity of 14MWh, and the first Attack-class boats will have LAB main batteries with a nominal capacity in the order of 20-30MWh).

It is unlikely that an LAB-equipped submarine will be able to match (let alone exceed) any major parameter of performance or capability of an LIB-equipped submarine entering service in the mid-late 2040s.

Naval submarine designers are already considering future all-battery submarines (UDT-Global2018 Nevesbue-Moray presentation) that will completely dispense with onboard charging capability, enabling zero indiscretion missions with very stealthy performance, significantly improved reliability, availability and safety at lower capital and operating costs.

It is conceivable that small coastal defence submarines of this type will be operational in the Indo Pacific Submarine Operating Environment (IPSOE) as early as the late 2020s/early 2030s, with all-battery “gigabattery” long range expeditionary submarines entering service in the 2050s. These all-battery submarines will be capable of undertaking complete missions with zero indiscretion and very low acoustic and thermal signatures.

Conclusion


With the commissioning of JS Oryu the lithium-ion main battery naval submarine is now an operational reality and no longer a matter of hypothetical speculation. JS Oryu appears to have met all of the JMSDF’s criteria for acceptance into operational service, and without any significant delays.

In the early 2020s JS Oryu and JS Toryu will provide real-world operational evidence of the performance of lithium-ion batteries in the main battery submarine propulsion role, and the actual level of improvement over LAB-equipped submarines of comparable design, size and capability.

Their operational performance will directly inform the design and development of a more advanced class of LIB-equipped attack submarines that will enter service in the early 2030s.

The continuing high rate of evolution of LIB and advanced LMB technology in the coming decades will result in new generations of advanced naval submarines that will completely outclass their LAB-equipped predecessors in all aspects of performance and capability by the mid-late 2040s.

The advent of the all-battery submarine will create a new class of submarine that will match or outperform even nuclear-powered submarines in many aspects of performance and capability by the 2050s.

David Glynne Jones & Derek Woolner
May 2020

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Coming soon


Posts on:
  • The suitability of light metal battery technology for naval submarine propulsion – a more detailed technical exploration of the use of light metal batteries in the main battery role for naval submarines
  • The evolution of the light metal battery submarine – a look at the possible pathway of development from the “enhanced” conventional submarine to future generations of all-battery submarines without on-board charging
  • LOTE Collins – a look at the challenges, opportunities and options for the life-of-type-extension program for the Collins class submarines

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