‘REPMUS’ (Robotic Experimentation and Prototyping augmented by Maritime Unmanned Systems) is a Portuguese Navy (PN)-led, NATO co-hosted exercise – held each September off Troia, southern Portugal – focusing on maritime unmanned system (MUS) capability development. As NATO requirements to improve presence, mass, and capability at sea to offset Russian activity become more pressing, ‘REPMUS’ is stepping up from test and evaluation activity to OPEX-based development of MUS capabilities for integration into NATO task groups.
Anti-submarine warfare (ASW) is a core, returning capability requirement for NATO and its member state navies. Together, they are seeking to integrate MUS technology with manned capabilities to augment ASW operational output. Within the wider ASW requirement, MUS can provide mass, particularly for intelligence, surveillance, and reconnaissance (ISR).
To develop a conceptual and operational framework within which to grow NATO’s national and multinational capability to use MUS for ISR sensing in the ASW role, in February 2020 NATO established the ASW Barrier project under the NATO Smart Defence Initiative. In November 2020, a letter of intent was issued – now signed by 13 countries, including Australia, Canada, Denmark, France, Germany, Italy, the Netherlands, Norway, Portugal, Spain, Sweden, the UK, and the US – that initiated project development. Finland is an observer country. NATO Maritime Command (MARCOM) and the alliance’s Centre for Maritime Research and Experimentation (CMRE) are project partners.
The letter was a statement of common intent to meet the requirement for a deployable ASW barrier using modern, evolving unmanned technologies, Ian Danbury – ASW Barrier project secretary, and a retired UK Royal Navy commander – told the Naval Leaders’ ‘Combined Naval Event 2024’ conference in Farnborough, UK in May.
The ASW Barrier Project will assess different operational concepts that can be enabled by the mass, persistence, and technological innovation MUS offers. However, Danbury explained, the initial focus is on ‘hold at risk’, a concept involving static positioning of sensors as a barrier to monitor whether something is approaching or attempting to cross a particular geographic gap.
‘REPMUS’ has been used to test ASW barrier capability developments in an operational setting. “From a Barrier project perspective, REPMUS is our main OPEX opportunity,” said Danbury.
Many NATO (and partner) countries bring MUS vehicles to ‘REPMUS’. Crewed platforms include PN ships and submarines, NATO allies’ surface ships, and occasionally a NATO task group. The Troia peninsula is well suited to testing naval technologies, with shallow water landward of the peninsula and deeper water – including the Setubal Canyon – to the seaward side. The area is also covered by a Portuguese government ‘free tech zone’, which enables test and experimentation with new technologies.
At ‘REPMUS 2022’, testing of individual barrier components began.
At ‘REPMUS 2023’, an early barrier instantiation was established, using integrated sensors to test capability for detecting and tracking simulated submarine targets. This instantiation included laying a sonobuoy field and deploying extra-large autonomous underwater vehicles (XL-AUVs) carrying towed-array sonars.
Manned/unmanned integration in establishing a barrier was also practiced, with MUS platforms working with the Italian Navy’s ASW-focused FREMM frigate ITS Carabiniere.
Barrier testing will continue at ‘REPMUS 2024’, said Danbury.
The exercise will feature 37 uncrewed air vehicles (UAVs), 20 uncrewed surface vessels (USVs), and 36 uncrewed underwater vehicles (UUVs), alongside 15 naval ships and 10 research vessels.
For the Barrier project, Danbury explained, the focus will be on varied sensing techniques; developing command-and-control (C2) capability across the barrier; and building data connectivity networks.
As regards the overall ASW Barrier project aims in ‘REPMUS’, “The trick is to ensure we can collect the incredible amount of talent, the significant expertise that is brought to the exercise, and corral it for common effect to move the needle on what we want to do in ASW with unmanned systems,” said Danbury.
‘REPMUS’ is also a testing ground for NATO’s continuing development of Standardisation Agreement (STANAG) 4817, designed to deliver network protocols to support commonality and interoperability in underwater communications architectures. Under STANAG 4817, NATO is building for example the Common Autonomy Tasking Layer (CATL) protocol, which focuses on information sharing between MUS vehicles; CATL then feeds into the Command, Control, Communication Maritime Robotic Exploitation (C3MRE) network, contributing to a common picture of UUV positions.
As regards the ‘REPMUS’ ASW serials and vignettes, Danbury explained there is intent to set the ASW Barrier concept into wider operational requirements. “[We will support] in the last few days of the exercise a truly tactical set of vignettes and scenarios, where ASW is an integrated element in a wider warfare vignette.”
“The concept of bringing the ASW Barrier component into the wider warfare vignette is to experiment with integrated C2 across a multi-domain battlespace, and to ensure that an ASW barrier is reactive to the changing situation and threat as it develops, to support overall objectives.”
Ian Danbury – ASW Barrier project secretary, and a retired UK Royal Navy commander
