1. Introduction
Just as militaries are trying to keep their vehicles, airplanes and ships undetectable above the surface with stealth technology, they try to avoid getting detected beneath the waterline. Under water, besides emitting systems such as the own active sonar, basically every moving or vibrating part of a vessel makes it detectable for adversary sonar. The main issue here is the propeller – the only widespread propulsion system in commercial and military vessels.
In this brief papier I aim to give an overview of the developments towards silent propulsion systems and the current state of the technology, particularly in relation to submarines, on the one hand, and its relative importance for global security on the other. As the existing technologies are still in the development phase, or at least not yet in widespread use, it is in the nature of things that much of the information is not publicly available. Furthermore, there is hardly any literature on what influence the exact technology has or could have on military planning.
The basic idea of silent propulsion is not entirely new. In the 1990 film “The Hunt for Red October”[1], an adaptation of the 1984 novel of the same name, a new Russian submarine with a noiseless magnetohydrodynamic propulsion called “caterpillar drive”, heads for the U.S. In the following sections we shall examine whether this idea remains science-fiction in 2024 or has become plausible reality.
2. The Technology
Besides purposefully created/shaped material items and objects, also knowledge and social practice is obviously an important element of technology. For example, ships need a knowledgeable and skilled crew, or at least a designer, to program automated control systems in advance so that they are ready for use. In order not to dwell too long on general discussions of definitions, we will assume here a definition of Martin Bridgstock for this paper. According to him, the definition of technology is “a body of skills and knowledge by which we control and modify the world.”[2] A noiseless propulsion system easily falls under this definition as you will realize when you read the paper at the latest. To be precise, silent drive can potentially be achieved through different propulsion systems - we will examine three of them in the following.
2.1 Silent Propellers
Silent Propeller technology is the one that is closest to existing conventional propulsion systems, as it still uses outboard propellers. The noise reduction therefore results from an improved design of existing propeller systems. This kind of noise reducing propulsion is already in use for some years and is applicable to conventional fixed pitched and controllable pitched propellers. For example, the Norway-based “Kongsberg Maritime” company is, in a cooperation with Dutch “Damen Naval”, delivering new frigates for the Dutch and Belgian navy from 2028 on. According to Kongsberg, the propulsion system has been optimized particularly for noise signature.[3] While there is no information on if and to what extend the technology is also used in submarines, there is at least a patent application for a silent propeller for submarines with the European Patent Office (EPO) under the classification “B63G 8/ Underwater vessels, e.g. submarines” and with the World Intellectual Property Organization (WIPO).[4] It is also possible to mount propellers in an outer water passing channel, in various lengths, to further reduce noise.[5]
2.2 Linear Induction Drive
Unlike propellers, a linear induction drive (LID) system would not have external moving parts. As far as research of publicly available information has shown, no submarine with such a propulsion system is in service as of now. There is only one fairly comprehensive theoretical calculation in a paper on how to use the basic LID-technology for a submarine propulsion system.[6] The paper suggests using the higher conductivity of hot seawater from the coolant system of the submarines nuclear reactor to generate thrust as (silent) propulsion.
The technology is at best in a theoretical phase and is based on nuclear reactors as an energy source. Realistically, it could therefore only be used in Supercarriers and nuclear submarines. Since Supercarriers can be easily localized in other ways, only nuclear submarines would come into consideration anyway. In view of the lack of prospects for practical application in a predictable time horizon, we will refrain from assessing its implications for global security.
2.3 Variable Buoyancy Engines and the Manta Ray Submarines
The Manta Ray is a submarine concept from the Defense Advanced Research Project Agency (DARPA) and Northrop Grumman, that underwent its first sea trials in March 2024 and is described as a long-duration, long-range, extra-large, payload-capable glider for undersea missions without need for on-site human logistics.[7] Variable Buoyancy Drive (VBD) is not limited to Manta Ray submarines. However, they are the most important or probably the only ones currently relevant to the global security architecture. Although the Manta Ray is an overall concept that combines numerous innovations such as the fully autonomous control system, the hydrodynamic shape or the modular design, we are focusing on one crucial component, the silent Variable Buoyant Drive. This propulsion does not require a propeller but uses changes in buoyancy and internal mass shifting to ascend and descend forwards through the water.[8] However, when looking at existing small scientific underwater drones using VBD, it is clear that this propulsion is much less powerful than conventional engines. Therefore, the Manta Ray has two small propellers as photographs show. Those are likely to provide auxiliary power when necessary and practical. The primary function of these propellers is probably to adjust the pitch angle of the drone, enabling it to ascend or dive, and to rapidly propel the drone upward when it encounters danger.[9]
3. Application
While silent propellers reduce the noise (approx. 10-15 dB), they do not eliminate it and therefore do not achieve the ultimate goal of noiselessness.[10] As they still do have an effect and are already in use in navy vessels, they obviously have a military application. The concept has meanwhile also become available for commercial vessels in order to reduce the effect of underwater radiated noise on marine life – it is therefore already a dual use technology.[11]
A submarine with VBD, the unmanned underwater vehicle (UUV) Manta Ray on the other hand, had its first successful sea trial earlier this year. As it is the most high-end technology with a practical application and comes closest to - or even achieves the goal of - a silent propulsion, it is the most interesting technology and probably has the greatest impact on the security architecture. Therefore, this will be our focus.
4. Implications for Global Security – Military Capabilities
While implications for the global security architecture are manifold and in their entirety beyond the scope of this paper, I will give an overview about the impact on the actual military capabilities. The biggest shift in naval power affecting the global security architecture is Chinas quantitative and qualitative naval superiority in the Indo-Pacific at the expense of the USA.[12]
After the U.S. forces were defeated in the Vietnam war, some popular critics questioned the military value of high-tech weapons systems, suggesting that the USA might benefit more from focusing on quantity over quality,[13] others have taken an opposite view.[14] When it comes to VBD technology, it can be concluded that this innovation is what makes the entire Manta Ray system viable. It opens up the possibility of equipping it with valuable and critical payloads, even in the absence of the strong in self-defense and fast traditional submarine platform. The Manta Rays, which are modular in design and approximately 20 meters wide[15], offer a cost-effective alternative to traditional submarines. While specific cost information is not available, it's clear that the construction and operational expenses of these autonomous systems are significantly lower than those of a conventional submarine, which can be up to 170 meters long and require a crew of around 150 sailors. This in turn creates the opportunity to, although being a high-end weapon system, build more single units thereof. This combines in an interesting manner quantity and quality which have often been seen as a trade-off. A glimpse into the scale at which the US intend to operate UUV is provided by the Chief of Naval Operations Navigation Plan. According to this, the US Navy intends to operate 150 unmanned platforms which shall “rebalance the fleet away from exquisite, manpower- intensive platforms toward smaller, less-expensive, yet lethal ones.”[16] This plan has been drafted 2021, hence years before the sea trials of the Manta Ray. A successful Manta Ray program would probably increase the number of the desired UUV`s in the future.
Besides quantity and quality of the platforms, also readiness, experience, strategy and other factors determine naval power. VBD in the Manta Ray will, additionally to the quantity and quality, potentially bring a strategic shift to the table. The Fisher Revolution and the Flotilla System revolutionized naval warfare before World War 1.[17] Today, a single undetectable Manta Ray vessel does not require protection from other ships and can approach an enemy and destroy it on its own. In addition, a larger area than today can be covered by the ability to operate a large number of stand-alone units.
The development of the Manta Ray System with all its sub-technologies also fits into the logic of AUKUS,[18]which consists of two pillars. Pillar one focuses on Australia acquiring nuclear-powered attack submarines and regular rotations of UK and US submarines in Australian ports, pillar two provides for collaborative development in six technological areas, including undersea capabilities, artificial intelligence and autonomy and electronic warfare; and in two broader functional areas: innovation and information sharing.[19]
Altogether, the VBD opens up the possibility to successfully run the Manta Ray program which in return could help re-shifting the balance of naval power in the Western Pacific, which has been altered in favor of the Chinese Navy.
5. Conclusion
The development of silent propulsion systems for maritime vessels, particularly submarines, represents a significant advancement in naval technology with profound implications for global security. As explored in this paper, silent propellers and variable buoyancy engines offer varying degrees of noiseless operation, which is critical for maintaining stealth in underwater environments. Among these, the VBD technology used in the Manta Ray project stands out due to its innovative design and potential impact on naval warfare. The ability to operate unmanned, autonomous submarines with minimal noise signatures could revolutionize military capabilities, allowing for a greater number of smaller, more cost-effective, and less detectable vessels to be deployed. This could lead to a strategic shift in naval power, particularly in the Western Pacific, where the balance of power is increasingly contested. The Manta Ray program, if successful, may play a crucial role in the future of naval operations, aligning with broader defense strategies such as those outlined in the AUKUS agreement. In conclusion, the pursuit of silent propulsion technologies not only enhances the stealth capabilities of submarines but also has the potential to reshape naval strategies and power dynamics on a global scale.
[1] Hunt for Red October, directed by John MacTiernan (1990; Los Angeles CA: Paramount Pictures Corporation, 2003) DVD.
[2] Martin Bridgstock, “Introduction,” in Science, Technology and Society: An Introduction (Cambridge: Cambridge University Press, 1998), 6, https://doi.org/10.1017/CBO9780511620034.
[3] ASDnews, “Kongsberg Secures Contract to Supply Propeller Systems to Damen Naval for 4 Anti-Submarine Warfare Frigates" last accessed August 13, 2024, https://www.asdnews.com/news/defense/2024/04/19/kongsberg-secures-contract-supply-propeller-systems-damen-naval-4-antisubmarine-warfare-frigates.
[4] European Patent Office, “Bibliographic data: CN215285218 (U) ― 2021-12-24” last accessed August 13, 2024, https://worldwide.espacenet.com/publicationDetails/biblio?FT=D&date=20211224&DB=EPODOC&locale=&CC=CN&NR=215285218U&KC=U&ND=; WIPO, “Patent Scope: 1. CN215285218 – Silent Propeller” last accessed August 14, 2024, https://patentscope.wipo.int/search/en/detail.jsf?docId=CN346911520&_cid=P10-LZTQT5-35193-1.
[5] Compare: WIPO, “Patent Scope: 2. CN111268073 – Submarine using shaftless magnetic levitation ultra-high-speed silent propeller” last accessed August 14, 2024, https://patentscope.wipo.int/search/en/detail.jsf?docId=CN297657869&_cid=P10-LZTQT5-35193-1 and Kongsberg, “Super silent tunnel thruster” last accessed August 14, 2024, https://www.kongsberg.com/maritime/products/propulsors-and-propulsion-systems/thrusters/super-silent-tunnel-thruster/.
[6] Sherif M.E. Ismaeel, “New Applications for Linear Induction Drives Used for Silent Propulsion Systems in Nuclear Submarines and Supercarriers” in: Arab Journal of Nuclear Sciences and Applications, 53:3 (2020) 252-266, DOI:10.21608/ajnsa.2020.15711.1250.
[7] Northrop Grumman, “Manta Ray”, last accessed August 16, 2024, https://www.northropgrumman.com/what-we-do/sea/manta-ray.
[8] National Research Development Corporation of India, Technology Details – Variable Buoyancy Engine, last accessed August 16, 2024, https://www.nrdcindia.com/technologyDetals/398/VARIABLE%20BUOYANCY%20ENGINE#:~:text=The%20Variable%20Buoyancy%20Engine%20(non,the%20buoyancy%20of%20the%20system.
[9] Huang Haocai, Sheng Chaowu et al., “Hydrodynamic analysis and motion simulation of fin and propeller driven manta ray robot”, in: Applied Ocean Research, 108 (2021) https://doi.org/10.1016/j.apor.2021.102528.
[10] Compare: Kongsberg, “Blade Air Emissions System”, last accessed August 16, 2024,https://www.kongsberg.com/contentassets/58f6ac359e1f4fe08435024ba532c39d/09.propeller-1p-28.01.20.pdf.
[11] The Royal Institution of Naval Architects, ”Kongsberg Extends Scope of Silent Propellers”, in: Naval architect, 1: (September 2019), 10.
[12] Congressional Research Service, “China Naval Modernization: Implications for U.S. Navy Capabilities—Background and Issues for Congress, updated January 30, 2024“, last accessed August 16, 2024, https://crsreports.congress.gov/product/pdf/RL/RL33153/277 ; James E. Fanell, The changing nature of naval power in the Pacific, last accessed August 16, 2024, https://www.gisreportsonline.com/r/naval-power-pacific/.
[13] James Fallows, National Defense, in: “Political Science Quarterly”, 96:4 (Winter 1981) 669–670, https://doi.org/10.2307/2149901.
[14] Robert L. Paarlberg, Knowledge as Power: Science, Military Dominance, and U.S. Security in: “International Security” 29:1 (2004), 122.
[15] Own estimates based on photographs.
[16] US Navy, “Chief of Naval Operations Navigation Plan 2022“, 10, last accessed August 16 2024, https://media.defense.gov/2022/Jul/26/2003042389/-1/-1/1/NAVIGATION%20PLAN%202022_SIGNED.PDF.
[17] Compare: Michael C. Horowitz, The Diffusion of Military Power: Causes and Consequences for International Politics (Princeton: Princeton University Press, 2010) 134-165.
[18] AUKUS is an acronym for Australia – United Kingdom – United States and represents their trilateral security partnership intended to promote a free and open Indo-Pacific that is secure and stable.
[19] US Department of State, “AUKUS: A Commitment to the Future“, last accessed August 16 2024, https://www.state.gov/aukus-a-commitment-to-the-future/.
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