As It Was Written, So Shall it Be: The coming of the SSE (Part II of 'Six Years On')

Submarines with LMB energy systems have now emerged as the standard for conventional designs. The pace and extent of their future capability and performance is already foreshadowed by commercial battery development. This will lead to the emergence of the all-electric submarine, the SSE, as coastal boats in the 2030s and as a fully transoceanic design by the 2050s, challenging the superiority of nuclear-powered submarines in regional waters by mid-century.

In Part 1 we described the current emergence of new submarine construction programs with energy requirements provided by Light Metal Batteries (LMB), primarily lithium-based battery chemistries. Submarines with LMB energy systems are now in operational service and we outlined that by 2030 some 20 submarines with such systems could be deployed in the Indo-Asia-Pacific Submarine Operating Environment (IAPSOE). Numbers could conceivably rise to more than 60 by 2040. It’s also expected that significant numbers of LMB-powered autonomous underwater vehicles (AUVs) will be operating in the IAPSOE.

Evaluation of LMB technology to provide the main battery for naval combat submarines began in Japan and the Republic of Korea in the early 2000s. Their advanced industrial economies allowed extensive technological cooperation across civil and military sectors evaluating lithium-ion (Li-ion) and lithium ferro phosphate (LFP) technologies. Over a decade later, at a time before it designed the LAB powered Attack class for the RAN, Naval Group was investigating LMB technology.

Experience with the first-generation of LMB-equipped submarines, which should become common by around 2030, has confirmed their submerged patrol endurance is typically twice that of a conventional LAB equipped submarine, with around three times the submerged high speed endurance. Improved efficiency while recharging should yield a 15 to 20 percent extension in snort range.

The pace of commercial LMB development continues to underwrite consistent improvement in performance and affordability, driven by a demand that has doubled every two to three years. Cell-level energy densities have been improving by ~ 4-5% annually since the early 1990s (~ 50% per decade), while pack-level energy densities have been improving by ~ 7% annually (~ 100% per decade) since 2008. This commercially driven process will allow substantial performance upgrades for LMB-equipped submarines at each major docking.

A decade or so ago, submarine planners and designers realised that LMB main battery capacities could increase within a few decades to the point where on-board charging with air-dependent generators was no longer feasible or necessary, leading to the development of a new class of all-electric submarines (SSE) with transformational capability and performance.

In 2018 the Dutch firm Nevesbu published its feasibility study into an all-electric battery submarine. The study found that an all-battery submarine could achieve a zero-indiscretion coastal patrol endurance of 24 days with available LMB technology, and that this could improve to more than 40-50 days as LMB energy densities improved.

The study identified significant tactical advantages for the all-battery submarine including:

• a fully air-independent energy system for propulsion and on-board systems (requiring no retreat from the patrol area to recharge)

• reduction in signature (thermal, acoustic, visual, radar)

• improved safety characteristics

The study also identified significant potential benefits resulting from the reduction of complexity, including:

• easier design and construction

• simplification of on-board systems

• reduced maintenance

• reduced crew workload

• improved availability and reliability

In 2019 Nevesbu published a follow-on study that evaluated both all-battery and battery/fuel cell energy systems.

In 2019 Hyundai Heavy Industries (South Korea) launched the HDS-400 next-generation midget submarine, equipped with lithium-ion batteries and foreshadowing a very significant increase in the capabilities and performance of small coastal submarines by the late 2020s/early 2030s.

In 2020 Naval Group (France) revealed its concept SMX-31E all-battery electric submarine, a Collins-sized boat with 40 days zero-indiscretion submerged endurance at 8 knots and up to 60 days at 5-6 knots.

SMX-31E is designed for successful operation in a post-2040 subsea environment, including:

• permanent oceanic surveillance

• advanced AI technology

• distributed subsea networks

• data monitoring from remote sensors

• large and smaller AUVs

Significant features of the SMX-31E concept design include:

• stealthy hull shape to minimise sonar detection

• very low thermal and noise signatures

• flooded hull design with separate pressure hulls for major functional areas

• ‘hangar’ space for AUVs including XL-AUVs

• unmatched electrical storage capacity with batteries located both in pressure hulls and externally (pressure-tolerant batteries)

• advanced data and AI systems for combat and sensor systems

• small operational crew size (less than 40% of Collins)

• shaftless electric rim drive ducted propulsors

Naval Group have been promoting this concept submarine to regional navies as an alternative to nuclear-powered submarines, and expect that an operational version will be available in the early-mid 2040s.

More immediately, SSEs are deploying in the mid-2020s in the form of Autonomous Underwater Vehicles (AUVs) with LMB energy systems, and the RAN’s Ghost Shark XL-AUV is a leading example of this development.

Key features of the Ghost Shark XL-AUV include a modular flooded hull design that can be configured with mission-specific payloads, advanced AI support for navigation, sensor and combat systems, operation from shore bases or surface ships, and pressure-tolerant lithium battery systems that enable operation at depths down to 6000 metres.

Developed on-budget and ahead of schedule through a partnership between Anduril Australia and the RAN as the first major initiative of the Advanced Strategic Capabilities Accelerator (ASCA) program, production and deployment of the Ghost Shark XL-AUV will commence in 2026. Ghost Shark XL-AUVs will be used for a wide range of tasks including “persistent, long-range and stealthy intelligence, surveillance, reconnaissance, and strike operations”.

The short development cycle and rapid improvement of key technologies would indicate that a 2nd-generation Ghost Shark with significantly increased capabilities and performance could be operational by the mid-2030s, and that this class of submarine will be a key element of Australia’s subsea defence capability by the mid-2030s or earlier, providing critical complementary support for the RAN’s existing crewed submarine force.

China is already deploying LMB-equipped AUVs, and has been evaluating the potential of both uncrewed and crewed small coastal SSEs since 2018. In 2022 China launched its “Olympic” class small (50 metre, 500 tonne) submarine, and although there was no formal announcement it appears that it may be a LMB-equipped SSE.

By the 2030s an Olympic class littoral SSE could have a zero indiscretion submerged endurance of around 25-30 days and full speed submerged endurance of 12-18 hours, translating into a quick response range of 240-360 nautical miles.

China has the capacity to commission such vessels by the early 2030s. Quieter than an SSN and with very low thermal signatures, China has the capacity to build the Olympic class in volume, deploying them as “sea lice” to excluding foreign SSNs from coastal waters that China wishes to control, most obviously those around Taiwan.

A clear timeline for the development and operational deployment of SSEs is now emerging:

• autonomous uncrewed SSEs from the mid-2020s

• coastal SSEs (250-1000 tonnes) by the mid-2030s

• regional SSEs (1500-3500) tonnes by the mid-2040s

• expeditionary SSEs (4000-5000+ tonnes) by the mid-2050s

All-battery LMB electric submarines (SSEs) will transform the capability, performance, affordability and sustainability of non-nuclear powered submarines through:

• full mission zero indiscretion operation

• lower costs for design, construction, operation and sustainment than SSKs or SSNs

• reduced maintenance requirements, faster turnaround and higher availability than SSKs or SSNs

• very large submerged energy capacity to support advanced AI & data systems and AUVs

• smaller crew sizes than SSKs or SSNs

• significantly lower thermal, noise and sonar signatures than SSKs or SSNs

• potential to operate at pressure depths greater than SSKs and comparable to SSNs

The consequence of these developments is that the capability and performance gap between SSEs and SSNs will be narrowing significantly by 2040, and that SSNs may have little or no performance advantage over SSEs when operating in constrained regional waters by mid-century, well before Australia’s SSN fleet is fully deployed.

By the time Australia may be able to sustain a couple of SSNs on operations they will find their operational envelope constrained by scores of SSE boats - friendly, suspicious or hostile - but with a presence that will limit the effectiveness of the RAN’s submarine operations.

All-battery LMB electric submarines (SSEs) will shape the strategic environment in which Australia will attempt to achieve its defence objectives. We will discuss this in more detail in Part III.

Derek Woolner and David Glynne Jones

6 October 2025