Virginia-class subs are pushing stealth boundaries, challenging Russia's ultra-quiet AIP technology beneath the waves. Who truly rules the silent depths?
by Kris Osborn, Warrior
Many nuclear powered attack submarines are fast and maneuverable to an extent that greatly improves survivability as it enables the boats to reposition quickly when under threat or maneuver as needed to elude incoming attacks. However, while many details related to US Virginia-class submarine “quieting” technologies are not likely available for security reasons, the technological advancement of the Block III and beyond Virginia-boat may enable their undersea signature reduction attributes to rival the ultra-quiet Air Independent Propulsion submarine technologies used by Russia and Japan.
Japan Soryu-class
In fact, the Japanese Maritime Defense Force’s Soryu-class submarines could be among the stealthiest to ever exist thus far, 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 More Survivable?
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 according to the TNI essay.
For all its advantages, AIP submarine propulsion may not ultimately be able to compete with high-speed, deeper depth Virginia-class submarines due to advanced detection technologies woven into Block III and beyond and additional “quieting” technologies built into the boats. The range and speed of nuclear-powered Virginia boats may be preferred for high risk areas such as the Pacific where a vast-expanse of ocean requires long-range, high-speed submarines.
Most Block III Virginia-class boats now operate with new engine-quieting technologies engineered to lower a boat’s acoustic signature, new coating materials intended to make it much more difficult for undersea sonar “pings” to generate a return signal or rendering and new antennas which enable communications while lowering the boats emissions. The Virginia-class Block III submarines also operate with a next-generation Large Aperture Bow sonar able to lower acoustic emissions by operating in passive “mode” at great distances.
Soryu-class
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. Given that the US Navy has been massively increasing the stealth capacities of its Virginia-class boats, 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.
Kris Osborn is the President of Warrior Maven – Center for Military Modernization. Osborn previously served at the Pentagon as a highly qualified expert in the Office of the Assistant Secretary of the Army—Acquisition, Logistics & Technology. Osborn has also worked as an anchor and on-air military specialist at national TV networks. He has appeared as a guest military expert on Fox News, MSNBC, The Military Channel, and The History Channel.