Key point: Certain basic technologies found in everyday devices can be used as the foundation for advanced military systems.
On October 4, 2018, the shattering of a bottle of sake at the Kobe Shipyards of Japan heralded not only the launch of a new submarine, but the dawning of a new era in submarine warfare—using a bit of technology you’re probably carrying in your pocket.
The Oryu (“Phoenix Dragon”) is the eleventh launched of Japan’s Soryu (“Blue Dragon”)-class submarines—a large design measuring 84-meters long that carries a crew of sixty-five and displaces 4,519 tons submerged. In many respects, the Soryu’s capabilities are typical of conventional submarines: it’s armed with six 533-millimeter tubes which can fire up to thirty Type 89 torpedoes or Harpoon anti-ship missiles and has a top underwater speed of twenty knots. Its range of 6,100 nautical miles lags a bit behind peers, while its maximum diving depth of 600 meters or greater is well above average, exceeding the crush depth of some anti-submarine torpedoes!
Despite their size and hi-tech trimmings such as a maneuverability-enhancing computer-controlled X-shaped rudder, two advanced acoustic decoy launchers and an extensive coating of sound-canceling tiles on the hull, the Oryu costs about $536 million—one-fourth to one-sixth the cost of a U.S. Virginia-class nuclear powered attack submarine. But Oryu stands apart from her predecessors because she’s the first large submarine to use lithium ion batteries—the same technology used in your smartphone and laptop computer.
Modern conventional submarines use electricity to turn the screw of their propellers and power their combat systems. This electricity is produced by diesel engines and generators and stored in hundreds of lead acid batteries. However, diesel engines consume a submarine’s air supply, forcing the sub to periodically surface, or snorkel close to the surface, and recharge its batteries in an ‘indiscretion period’ in which it is exposed to easier detection and destruction.
Furthermore, submarines generators are fairly noisy. For that reason, a submerged submarine operating in close proximity to enemy forces may turn off its diesel engine and run purely on battery power.
The problem is that a sub drains away its battery really quickly. A conventional submarine racing at maximum speed (usually around twenty knots) will exhaust its battery in an hour or two. At a sustainable cruising speed of five to ten knots, that endurance may extend to a few days. One way around this is to use nuclear power, which provides near limitless underwater endurance, allows higher speeds and is quieter than running diesel engines. However, it’s not as quiet as a diesel running purely on batteries, and the nuclear subs can’t switch off their reactors operationally. More importantly, nuclear powered-submarines costs four to six times as much—and even for countries with access to nuclear reactor technology, they’re overkill for short-range patrols.
In the last two decades, advancements to conventional submarines have focused on supplementing diesels with various quieter and longer-enduring Air Independent Propulsion schemes. The previous seven Soryu-class submarines included Stirling closed-cycle heat engines—a technology first pioneered by the Swedes, and now found on Chinese Type 039A submarines too! AIP submarines can run more quietly than nuclear submarines and can remain submerged for weeks before needing to surface, though only while traveling at low speeds of four to six knots. However, downsides include bulkiness and the risks posed by volatile fluids used to operate them.
The Oryu and her successors herald a different approach—increasing battery life. In 1991, Japanese companies introduced lithium-ion batteries into general commercial use. Since then, they have skyrocketed in popularity for their application to portable electronics including laptops and cell phones. Compared to traditional lead-acid batteries, lithium-ion batteries have greater energy density for their volume and weight, can charge a lot faster, and discharge their energy with 80 to 90 percent efficiency, compared to roughly 60-70 percent for lead batteries.
Now, one may recall that a landed 787 airliner caught fire in Boston’s Logan Airport in 2013 due to an overheating lithium-ion battery, or that the same type of battery was notorious for causing Galaxy S7 tablets to spontaneously combust. Obviously, the tendencies of such batteries to ‘run away’, overcook themselves and catch fire would also be a nightmarish concern on a submarine packed with hundreds of batteries in close proximity! Indeed, a lithium-ion battery in a U.S. SEAL Delivery Vehicle mini-sub also caught fire in Pearl Harbor in 2008. This explains why LIB technology hasn’t been implemented on a large submarine sooner.
Japan, therefore, has thrown a lot of money and years of effort into building greater safety and reliability into its sub-based lithium-ion batteries by implementing improved battery-cell matrices with hardened dividers, stabilized chemicals and automatic fire extinguishers, and has reportedly tested the configuration rigorously to account for various high-stress scenarios such as exposure to seawater. The the launch of the Oryu suggests the Japanese military is satisfied that the lithium-ion batteries have been refined it into an operationally viable and safe capability.
The Oryu’s 672 LIB-modules reportedly afford it twice the battery life of the 480 lead-acid batteries in the prior variants—meaning it may be able to cruise for around before needing to surface. Furthermore, it can recharge its batteries much faster, meaning the sub will have brief “indiscretion periods” while recharging batteries—a decrease from 2.7 hours to 1.4 hours according to one calculation. The LI-batteries do come at a higher cost $97 million, compared to $13 million for the lead-acid batteries.
An LIB submarine’s underwater endurance may also not necessarily equal the multiple weeks an AIP-powered submarines is capable of. However, the greater battery life would give a submarine captain more flexibility on using more electricity for longer ultra-quiet stretches with the generators off, or for longer periods high-speed maneuvers. Overall, LIB alone may be more useful than AIP for submarines dispatched on short-range patrols.
It’s also worth noting that there’s no reason that lithium-ion batteries couldn’t be combined with AIP systems such as fuel cells for the best of both worlds—the principal downside being additional cost and space sacrificed to accommodate the AIP engines.
Kawasaki Heavy Industries will build one additional Soryu-class submarine with lithium ion batteries—the twelfth and last—and then Japan will begin developing a next-generation LIB-submarine. Some reports indicate the earlier Stirling AIP powered Soryus may also be upgraded with LIB.
Meanwhile, there are rumors of renewed interest in the Soryu from Australia. In 2016, Canberra passed over the Japanese submarine in favor of the French Shortfin Barracude for its plans to build twelve replacements for its Collins-class attack submarines. However, disagreements over the extent of French cooperation (the Aussies want more of it), and changes in the governments of both Paris and Canberra have put the arrangement= in question. However, Australian submarines would need to patrol much further from home waters than Japanese boats, and an Australin Soryu-based design would need to be lengthened to accommodate extra fuel and enlarged crew accommodations.
Regardless, Japan’s apparent deployment of reliable submarine lithium-ion battery technology marks a second major leap forward in the capabilities of affordable conventional submarines in the last twenty years. South Korea and China are also developing LIB submarines.
While the U.S. Navy is wedded to the premium capabilities of its far more expensive nuclear-powered attack and guided-missile submarines, it remains unable to pay for and build them fast enough to maintain the target fleet of sixty-six. The potential of LIB-submarine should give the Navy yet another reason to reevaluate that choice given intensifying security competition with both China and Russia.
Sébastien Roblin holds a Master’s Degree in Conflict Resolution from Georgetown University and served as a university instructor for the Peace Corps in China. He has also worked in education, editing, and refugee resettlement in France and the United States. He currently writes on security and military history for War Is Boring. This first appeared in October 2018.