The following piece first appeared on Warrior Maven, a Military Content Group member website.
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The Japanese Maritime Defense Force’s Soryu-class submarines could be among the stealthiest to ever exist, as they are engineered with lithium-ion batteries and a non-nuclear diesel-electric propulsion system. They are also a little smaller than most existing attack submarines, in part for the specific purpose of being less detectable. The lithium-ion batteries enable the submarines to remain beneath the surface for longer periods of time than lead-acid batteries, something which reduces the risks associated with having to surface. The longer a boat can stay at depth, the less detectable it is.
Lithium-ion batteries, however, were not added to Soryu-class submarines until the 11th boat, and all previous submarines in the class used the extremely quiet Air Independent Propulsion (AIP).
Although the US Navy has prioritized nuclear propulsion, Air Independent Propulsion is survivable as it does not need to surface, and does not create the undersea noise generated by submarine nuclear reactors using pumps to circulate the reactor coolant.
The AIP propulsion in the Soryu-class is used to help support the boats’ diesel-electric engine, an engine described in a 2020 essay from The National Interest as unique, because it “uses bottled liquid oxygen so that the engine’s diesel fuel can combust. The advantage of this propulsion system is that it runs much quieter than a traditional diesel engine. Furthermore, its range is estimated to be around 6,100 miles or about 9,800 kilometers.”
The Soryu-class boats are not only extremely stealthy and quiet but also heavily armed with Type 89 torpedoes and UGM-84 Harpoon anti-ship missiles.
The following piece first appeared on Warrior Maven, a Military Content Group member website.
—
The Japanese Maritime Defense Force’s Soryu-class submarines could be among the stealthiest to ever exist, as they are engineered with lithium-ion batteries and a non-nuclear diesel-electric propulsion system. They are also a little smaller than most existing attack submarines, in part for the specific purpose of being less detectable. The lithium-ion batteries enable the submarines to remain beneath the surface for longer periods of time than lead-acid batteries, something which reduces the risks associated with having to surface. The longer a boat can stay at depth, the less detectable it is.
Lithium-ion batteries, however, were not added to Soryu-class submarines until the 11th boat, and all previous submarines in the class used the extremely quiet Air Independent Propulsion (AIP).
Although the US Navy has prioritized nuclear propulsion, Air Independent Propulsion is survivable as it does not need to surface, and does not create the undersea noise generated by submarine nuclear reactors using pumps to circulate the reactor coolant.
The AIP propulsion in the Soryu-class is used to help support the boats’ diesel-electric engine, an engine described in a 2020 essay from The National Interest as unique, because it “uses bottled liquid oxygen so that the engine’s diesel fuel can combust. The advantage of this propulsion system is that it runs much quieter than a traditional diesel engine. Furthermore, its range is estimated to be around 6,100 miles or about 9,800 kilometers.”
The Soryu-class boats are not only extremely stealthy and quiet but also heavily armed with Type 89 torpedoes and UGM-84 Harpoon anti-ship missiles.
Deterring China Undersea
The Soryu-class is now being succeeded by Japan’s emerging Taigei-class submarines, yet the fleet of Soryus could prove extremely significant in any US-Japanese campaign to stop a surprise People’s Liberation Army (PLA) amphibious attack on Taiwan.
The reasons for this are clear, in large measure because submarines may be the US best option to destroy a PLA Navy warship attack. Larger surface combatants can of course be easily seen from the air by drones and satellites, so China could in fact attempt to launch a surprise amphibious attack at a time when US and Japanese surface warships are outside of the range necessary to respond. Such a dynamic could to launch a surprise annexation of Taiwan, could give the PLA Navy the potential opportunity to seize or annex Taiwan before any US-allied force could respond.
Submarines, however, could change this equation, Japanese ultra stealthy and torpedo-armed Soryu-class boats could quietly lurk within striking range of PLA Navy surface warships in position to instantly attack. These could also be supported by US Virginia-class attack submarines.
The other reason why Soryu-submarines could make a huge difference relates to a pure numbers question; the US Navy continues to face a submarine deficit wherein Combatant Commander need for attack submarines massively outpaces available supply. This is particularly true of the Pacific, a key reason why Congress is working intensely with the Navy and its industrial partners to massively “uptick” or increase Virginia-class construction.
While the Los Angeles attack submarines are considered highly effective, they are retiring faster than Virginia-class boats can be added, as there are only 20 left. As more of these Los Angeles boats near the end of their intended surface life, the US Navy’s submarine deficit is expected to worsen in the next few years until larger numbers of Virginia-class boats arrive.
The quieting technology of the Soryu class cannot be understated, particularly in an era where newer non-acoustic detection technologies are improving submarine detection. At the moment, it is believed that the US has undersea superiority over China, however it may not be clear just how much longer that will remain the case.
The US Navy, however, is massively increasing the stealth capacities of its Virginia-class boats, and the combination of ultra-quiet Japanese submarines and US submarines could form a protective web across key parts of the Pacific. Perhaps regular forward patrols could protect both the Japanese coastline as well as the Senkaku Islands and Taiwan.
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