Given the heightened likelihood of inter-state conflicts and the proliferation of submarines around the world, anti-submarine warfare (ASW) has returned to the minds of military planners and decision-makers.
Traditional ASW is cost-intensive and implies a high level of expenditure; in terms of personnel and materiel. Forward-thinking industry and military stakeholders anticipate that large uncrewed surface vehicles (LUSVs) and extra-large uncrewed underwater vehicles (XLUUVs) will relieve crewed ASW assets from 2025 onward.
This article presents a naval systems’ OEM perspective on the operational and economic benefits of utilising non-organic uncrewed maritime systems in an ASW mission. Its intent is to accelerate the creation of operational concepts considering teams of large uncrewed systems. The ASW mission that we consider is performed in the North Atlantic to protect sea lines of communication (SLOC) from North America to Europe. However, the methodology and results of this article can be transferred to other regions, such as the South China Sea and the First Island Chain. A comparison of the analysed ASW operations shows a significant economic benefit (80% savings) compared to the use of maritime patrol aircraft.
The Scenario and Assets
Overlapping geographic spheres of interest shape naval deployments in the North Atlantic, in particular in the Norwegian and Greenland Seas. From a defensive point of view, NATO seeks to protect its SLOC from America to Europe, as well as critical maritime infrastructure for energy supply and data distribution in the North and Norwegian Seas. The Russian Armed Forces mainly seek to protect their nuclear at-sea deterrent in the Barents Sea, often called a ‘Bastion’. From an offensive point of view, both parties undertake every effort to hold each other’s assets at risk. The continental land mass and large islands frame this area of operation and form gaps of approximately 200 to 400 nautical miles (see map). These encompass the Bear Gap between Svalbard and continental Norway, and the Greenland-Iceland-UK or GIUK Gap. As submarines must pass through these gaps, these choke points offer the best chance of forming a submarine detection barrier.
NATO needs an all-year-round, persistent submarine detection capability in all weather conditions. The required capability can be provided by large uncrewed vehicles classified as XLUUVs and LUSVs. Such vehicles are not yet active performing the described task. However, prototyping such a capability within a timescale of three years seems to be a realistic prospect when viewed as a joint effort between the user and the system integrator.
The illustration below shows a concept for a small water-plane area single hull (SWASH) type LUSV able to operate in high sea states. It can deploy active and passive towed sonar and works in teams with other LUSV and XLUUV to create a bi- or multi-static sonar situation.
As examined in the comparison in the Fact Sheet, uncrewed solutions bring real advantages. In a further examination, we contrast traditional methods for ASW barrier operations with uncrewed options. The figure below shows the assets employed. The assets in the scenario form detection barriers in the GIUK Gap, in the Bear Gap and towards the entrance to the North Sea (where its multitude of infrastructure is covered). MPA-based detection uses 15 MPAs deployed from three airports. At every point in time five MPAs are on scene, deploying a combined total of 480 sonobuoys per day.
For the uncrewed scenario, a sonar performance simulation-based assessment of asset quantities leads to the need for 27 XLUUVs and ten LUSVs at sea. An expert assessment of typical usage upkeep cycles leads to a total need for 35 XLUUVs and 13 LUSVs. The Bear Gap is not protected by LUSVs due to the proximity of sophisticated anti-ship systems available to the opposition, instead depending on seven XLUUVs at sea. The XLUUV can achieve good sonar performance while remaining stealthy.
The graphic illustrations below show the calculated results of a multi-asset low-frequency active sonar operation leading to a high probability of detection across a wide area. One receiving (RX) XLUUV on each of the port and starboard sides of a transmitting (TX) and receiving (RX) LUSV form a team of three assets. The transmitter is a towed low frequency transmitter. The receivers are towed sonar arrays. The spacing between assets is 54 nautical miles. All the coloured areas indicate a detection of the submarine. With the suggested spacing, one uncrewed team could form a detection barrier in excess of 100 nautical miles. Differences between winter and summer water conditions seem to be negligible for this area and type of operation.
In this scenario, XLUUVs with typical conventional submarine towed array sonars patrol the Bear Gap. They operate in passive mode, listening for specific submarine signatures. The graphic illustrations below represent the lowest detection range results for winter and summer from more than 20 simulation runs with varying target and receiver depth, signal processing and in different seasons. The detection ranges of 41 nautical miles in March (best month) and 18 nautical miles in August (worst month) imply that seven XLUUVs at sea achieve a reasonable likelihood of detecting a submarine crossing the 370 nautical mile-wide Bear Gap.
The calculations shown verify the chosen number of assets for the uncrewed concept, providing a surveillance performance comparable to an MPA-based solution.
Today’s ASW is cost-intense in both capital expenditure (CAPEX) and operational expenditure (OPEX) terms. It binds capable assets with highly trained crews to an area of operations. This section compares the well-established MPA approach cost-wise to the uncrewed concept.
MPA mission costs consist of CAPEX for aircraft procurement and OPEX for operating the aircraft as well as sonobuoys, treated as a separate OPEX position. A representative mix of active and passive sonobuoys and prices from US Department of Defense publications yields realistic sonobuoy costs. For the P8-A Poseidon both CAPEX and OPEX derive from official US publications. 
For the uncrewed concept, an estimated CAPEX of EUR 2.5 Bn procures 48 assets – 13 LUSVs and 35 XLUUVs – as well as relevant infrastructure at three service hubs. OPEX for the LUSV / XLUUV solution considers fuel, spares, salaries, and significant capability enhancement activities at a total EUR 45 M per annum.
The graph below illustrates the cost advantage offered by a LUSV/XLUU concept compared with the traditional MPA approach. A striking feature is the inverted proportion of OPEX and CAPEX. MPA operations are OPEX-intensive whereas, for the uncrewed vehicle operation, CAPEX is higher than OPEX. In absolute figures, the monthly Total Cost of Ownership (TCO) for the MPA/sonobuoy approach amounts to approx. EUR 58 M whereas the monthly TCO for the LUSV / XLUUV concept amounts to approx. EUR 10 M.
An uncrewed anti-submarine warfare detection barrier seems to be an approach worth pursuing. The concept is adaptable and scalable towards different areas of operation and threat situations. It is affordable and based on near-future technology, delivering at sea capability within less than five years. Implementation is possible by individual or teamed countries or organisations such as NATO or the European Union.
Willem Hendrik Wehner, Jens Ballé and Klemens Ehret
1. Hudson Institute, Sustaining the Undersea Advantage: Disrupting Anti-Submarine Warfare Using Autonomous Systems. Washington D.C., 2020.
2. RAND Corporation, Enhancing deterrence and defence on NATO’s northern flank. Santa Monica, 2020
3. Department of the Navy, Department of Defense Fiscal Year (FY) 2022 Budget Estimates: Other Procurement, Navy May 2021
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