Portugal is the first country in recent history to operate a conventional submarine under the Arctic ice. The Navy's adaptations for this mission are being studied by Canada, which will incorporate them into its new fleet. Arpão has expanded "tactical options" for underwater combat in the far north.
Arctic sea ice, which has been monitored by satellites since 1978, has beenshrinking dramatically in recent decades. On 22 March, with winter already over, the period of greatest accumulation, the maximum extent for 2026 is thought to have been reached – 14.33 million square kilometres, according to the United States (US) National Snow and Ice Data Center (NSIDC). It is the lowest peak since records began, something now seen for the second consecutive year.
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With this region warming almost four times faster than the rest of the planet, new sea routes and business opportunities are opening up for many countries which have had their eye on the far north of the Earth for centuries, drawn by its remoteness and weather conditions, which are fertile ground for scientific research, but above all by the natural wealth stored there, from oil and gas to strategic minerals.
The latest report by the Arctic Council (source in Portuguese) points to a 40% increase in the number of individual ships operating in this area over the past 12 years, while the distance sailed has leapt by 95%, from 6.1 million to 11.9 million nautical miles. It is worth noting that these data include vessels from the eight Arctic states (United States, Canada, Iceland, Norway, Sweden, Finland, Denmark and Russia) as well as ships that regularly enter the area covered by the Polar Code under the flag of the Arctic Council’s observer states.
Although the melting caused by climate change is making the region more inviting for incursions by naval, cargo and cruise ships, navigation at high latitudes is far from straightforward. “In many respects, going into space is easier than piloting and operating ships in the polar regions,” writes (source in Portuguese) Ekaterina Uryupova, a researcher at the Arctic Institute.
On top of the challenges posed by growing vessel traffic, global warming is thinning the ice, leading to more glacier fragmentation and the formation of more icebergs. Even summer days are problematic: this is when melting intensifies as a result of higher temperatures.
Sea-ice floes drifting in the water are unpredictable, and when they collide, driven by winds or ocean currents, they pile up, forming “mountain ranges” of ice on the surface (“ridges”) and beneath the water (“keels”), with some underwater formations reaching several tens of metres. This is one of the main dangers for anyone taking part in submarine missions in the Arctic Ocean. If the submarine is conventionally powered, and therefore has limited underwater endurance, the risk is greater, because in areas of dense ice cover surfacing becomes impossible or much more difficult.
Submarine ArpãoSubmarine Arpão
There is also the threat of flooding or, more commonly, of fire. In an account given to The War Zone (source in Portuguese), a defence-focused website, Eric Moreno, a US Navy veteran and submariner between 2001 and 2008, explains that the more internal space a submarine has, “the greater the volume of atmosphere available to ‘absorb’ a fire”, which gives the crew “more time to react appropriately”. Conversely, he notes, the margin for manoeuvre is much narrower on a traditional submarine, which, being smaller and with limited headroom, is prone to a faster build-up of heat and smoke, compounding the difficulties of responding to an emergency.
Because it is a theatre of operations with extreme conditions, under-ice navigation in the Arctic has, since the late 1950s, been reserved for nuclear-powered submarines, most of them over 100 metres long, high-speed and with virtually unrestricted endurance. Portugal’s Navy, however, overcame all misgivings, including those of NATO allies, and between April and June 2024 sent the NRP Arpão into the depths of these icy waters, becoming the first in recent history to do so with a conventional submarine.
The crew of around 30 sailors, commanded by frigate captain Taveira Pinto, spent a total of four days beneath the ice sheet off Greenland, on a mission without precedent, both in terms of operational skill and in pushing back boundaries long deemed insurmountable. Portugal thus joined the US, the UK and Russia in a small group of countries that have already operated beneath the polar ice cap, though these powers have the advantage of nuclear-powered submarines.
“Operational competence of its own”
The NRP Arpão sailed from Lisbon Naval Base on 3 April 2024, as part of NATO’s Brilliant Shield operation, on a mission that lasted 78 days, supported by the US, Canadian and Danish navies, and comprised several stages, with a total of 1,800 hours at sea, 1,500 of them submerged.
After completing the first 22-day patrol, used to test new procedures and modifications, the vessel docked in the port of Nuuk, Greenland, to refuel and take on provisions. The voyage then continued north, crossing parallel 66º33’N, which marks the boundary of the Arctic Circle, with the then Chief of the Navy, Henrique Gouveia e Melo, on board, who had conceived this expedition more than a decade earlier.
Former Navy Chief of Staff Gouveia e Melo aboard the submarine Arpão in the ArcticFormer Navy Chief of Staff Gouveia e Melo aboard the submarine Arpão in the Arctic
After 39 hours and 30 minutes in deep submergence under the ice, the crew began exploring the ice sheet, which meant identifying natural openings for a hypothetical emergency surfacing, as well as monitoring the width and density of the frozen cover.
This feat by the Portuguese sailors was made possible by the air-independent propulsion, or AIP, technology (Air Independent Propulsion in English) fitted to Arpão – a fuel-cell system supplied with hydrogen and oxygen tanks that does not require fresh air to recharge the batteries and generates power underwater, allowing these diesel-electric, or conventional, submarines to extend their submerged time significantly, to two or three weeks depending on speed, making under-ice patrols possible.
Confidence in undertaking this mission stemmed from “a rigorous technical assessment that the platform had intrinsic characteristics compatible with this type of [Arctic] environment”, Portugal’s Navy told Euronews. But the venture would not have succeeded without “demanding preparation” over seven months involving an “in-depth study of the area” and “specific material adaptations” following an overhaul of the submarine’s systems.
In the official documentary on the mission, Gouveia e Melo recounts that Arpão’s crew came across “mountains” of ice stretching “ninety metres down” below the surface. These obstacles are part of what the Navy describes as a “complex combination of challenges”, from “fast ice, loose ice, icebergs” and “acoustic conditions very different from those in the open sea” to the “severe limitation of options in the event of an onboard emergency”.
One of the risk-mitigation measures was the installation of a high-frequency sonar, with support from the Hydrographic Institute (source in Portuguese), along with specific sensors to detect ice, measure its thickness and enhance navigational safety. Protective structures were also designed and fitted to the sail by Arsenal do Alfeite S.A. to prevent the most sensitive masts, notably the periscope and optronic mast, from colliding directly with ice floes.
Recalling that “sensors, engineering, training and doctrine were adjusted for a very specific and segregated theatre”, the Navy says it has shown allies that “Portuguese submarine capability is technologically mature, capable of learning quickly and adapting (…) in highly complex environments”.
US experts in under-ice operations (Ice Pilots) provided initial guidance, but it was the Portuguese who, “to a large extent”, took care of studying the region, preparing emergency scenarios, training the crew and making tactical use of the submarine’s sensors, the Navy stresses, which “shows a national capacity to analyse meteorological and oceanographic data, absorb allied knowledge and turn it into operational competence of its own”.
Where no Western submarine had ventured since the Second World War
Marginal Ice Zone in the ArcticMarginal Ice Zone in the Arctic
Submerged navigation at a depth that allowed the masts to be raised above the surface (periscope depth) in the so-called Marginal Ice Zone (MIZ) – Marginal Ice Zone in Portuguese – further underscored the merits of the Portuguese mission.
It was a manoeuvre that astonished allies, commander Taveira Pinto admits in the official documentary, calling it the high point of the operation. The MIZ is the zone where the solid ice pack meets open water and, because it is exposed to violent storms and huge waves, blocks of ice break up more quickly and follow unpredictable trajectories.
Since the Second World War, the Navy notes, no other Western submarine had dared operate in this “highly problematic” and very “uncertain” area, where “both detection and manoeuvre become more complex” because of “fragmented ice, floes of varying size, very high ambient noise and the presence of marine life, which degrades the normal use of sonar as the main safety sensor”.
Using instruments in this chaotic context is a particularly delicate task, not least because of the “associated physical risk”. Ice floes encountered here can be large enough to inflict structural damage if they come into contact with the vessel.
“That is why the technique developed by the NRP Arpão for returning to periscope depth made all the difference and allowed a traditionally avoided area to be turned into a space where it became possible to operate with an acceptable level of safety,” the Navy argues, stressing that the exercise provided “freedom of action” and made submarine operations in the Arctic more flexible.
Submarine Arpão in the Marginal Ice ZoneSubmarine Arpão in the Marginal Ice Zone
More than proving it can operate in a polar ocean, Arpão delivered “tactical innovation in a real environment”, with an “ability to adapt” in a “theatre where access, survival and discretion depend on very finely balanced decisions”. In doing so, Portugal “produced operationally relevant knowledge for allies”, set down in an Arctic navigation manual – a comprehensive base that makes the work easier for those who may in future decide to venture into the region.
Having charted unknown waters and been willing to take steps not initially backed by means and technology purpose-built for such demanding tasks, Portugal systematised this know-how in what the Navy describes as a “doctrinal tool” that sets out lessons drawn from real-world experience.
The publication delves into a range of variables, notably multidisciplinary preparation, the interpretation of acoustic behaviour in a scenario unfamiliar to the Portuguese, ice assessment and the adaptation of procedures in terms of safety.
These lessons are being taken on board by Canada, Portugal’s NATO ally, as it makes the necessary adjustments to its new submarine fleet and ensures that the boats are fit for operations in the Canadian Arctic, which accounts for 40% of the country’s territory and more than 70% of its coastline.
Arpão’s adaptations as a benchmark
“What struck me most was how the crew of NRP Arpão and the Portuguese Navy approached the mission. They were calm, professional and meticulously prepared,” Harrison Nguyen-Huynh told Euronews, a commander in the Canadian Navy who was on board Arpão throughout the 2024 operation as a liaison officer supporting the crew.
Harrison Nguyen-Huynh, Deputy Commander of Canada’s Submarine ForceHarrison Nguyen-Huynh, Deputy Commander of Canada’s Submarine Force
Praising the attitude and cooperative spirit of the Portuguese submariners, commander Nguyen stresses that this NATO exercise was another important opportunity for collaboration with allies “in order to gain insights into some of the challenges of operating in the North”.
Observing Arpão in “operations near, on and under the ice”, the Deputy Commander of Canada’s Submarine Force adds, will help Ottawa modernise its submarines, all the more so because “one of the main requirements” of the ongoing procurement programme is the “ability to operate in the Arctic environment”.
The project was launched in 2021 to study operational environments and then define the characteristics and technology of the Canadian Navy’s future submarines, which will replace the current fleet of four Victoria-class boats, bought second-hand from the UK in 1998 and scheduled to leave service by the late 2030s.
Former Canadian prime minister Justin Trudeau did not rule out nuclear propulsion, something the country’s defence authorities ultimately rejected because of the much higher cost.
In a statement (source in Portuguese) published in August 2025, the Canadian government, led by Mark Carney, confirmed its intention to buy up to 12 submarines, “with extended range and endurance that will provide stealth, persistence and lethality as key capabilities”. Canada, which has the world’s longest coastline – more than 202,000 kilometres – needs to be able to “detect, track, deter and, if necessary, defeat adversaries” in the country’s “three oceans”, the government added.
Even though conventional submarines are at stake, a project of this scale and ambition requires loosening the purse strings. Some estimates put the cost at 60 billion dollars (around 51 billion euros), although defence analysts have already forecast a total cost of around 100 billion dollars (close to 85 billion euros), the Canadian newspaper Ottawa Citizen (source in Portuguese) has reported.
According to the same newspaper, it could be the largest military procurement in Canada’s history. The government wants to fast-track the process and the contract could be signed this year, but the Canadian Navy estimated as early as 2025 that the first submarine would only become fully operational in 2037.
The new submarines will not initially have the full range of under-ice navigation capabilities for the Arctic, revealed Royal Canadian Navy vice-admiral Angus Topshee, quoted by the newspaper The Globe and Mail. This is where Portugal’s example comes in: the modifications and additions made to Arpão will guide the outfitting work to be undertaken after delivery, both in terms of the structure and of specialised equipment.
As commander Nguyen points out in his interview with Euronews, security is one of the priorities. The installation of protective structures to shield the masts and reinforce the sail, one of the main adaptations implemented by the Portuguese, is thus seen as essential to prevent structural damage and safeguard against a possible emergency scenario requiring the submarine to break through the ice.
ArpãoArpão
Another key element, Nguyen notes, is effectiveness, ensured to a large extent, in the case of the 2024 mission, by the specialised sonar on top of the sail, which was used to map the ice overhead and detect open water. Operations in the Arctic require a two-dimensional picture (above and below), and by incorporating this extra capability to monitor the glacial “ceiling”, Arpão provided much sharper maritime situational awareness.
For future Arctic missions with diesel-electric submarines, the Portuguese experience sets out important guidelines on carrying out static manoeuvres and understanding the specific characteristics of the marginal zone, where noise from moving ice affects sensor performance. The mixing of fresh and salt water can also influence how sound propagates and is analysed, the NATO Association of Canada (source in Portuguese) recalls. The recordings made by the Portuguese will therefore be an important resource, helping, for example, to identify false echoes near the ice and improve detection.
The Navy told Euronews that the results achieved by Arpão received a “very positive reception” among allies and that, after the mission, several meetings were held to share knowledge and “lines of action for future planning”.
“Sharing information and best practices with our allies strengthens our collective capability and increases the effectiveness of our operations,” says commander Nguyen, stressing that Canada, as an “Arctic nation”, views campaigns in the “North” as “essential” to protecting its sovereignty.
Conventional submarines as a means of fighting beneath the ice
At present, there are no plans for further Portuguese submarine missions in the Arctic, “because of other operational and strategic priorities”, says Navy spokesperson Ricardo Sá Granja in his interview with Euronews. Even so, Portugal remains alert to developments in the region, “where geopolitical competition is intensifying”.
The Arctic is, indeed, increasingly militarised. On its Kola Peninsula, which borders Norway and Finland, Russia has one of the largest concentrations of nuclear weapons in the world, and in those waters it operates submarines capable of carrying dozens of warheads each.
There has even been an increase in Russian submarine activity near the GIUK gap, a strategic chokepoint in the North Atlantic between Greenland, Iceland and the United Kingdom, crucial for accessing Atlantic waters from the Arctic. According to NATO commanders, activity levels here may now exceed those seen during the Cold War.
China, for its part, declared itself a “near-Arctic state” in 2018 and continues to invest in the “Polar Silk Road”, a plan to establish new commercial shipping routes across the Arctic Ocean and cut travel time between Asia and Europe to 18 days.
In the face of this escalation and jostling for position, Portugal’s Navy says it is committed to the “collective effort that contributes to stability” in the far north, but stresses that “deterrence and defence of the Euro-Atlantic area cannot be carried out in the abstract”.
Arpão in the ArcticArpão in the Arctic
The mission undertaken by Arpão also shows that Portugal and other countries, despite the constraints of conventional submarines, have the potential to play a more active role in undersea warfare, including that fought beneath the ice.
On the one hand, these vessels are limited by lower speeds and shorter submerged endurance; on the other, they can remain very quiet when running on batteries. That discretion is an advantage that can be exploited, in today’s more hostile context, for surveillance, intelligence and other operations.
Operating in the North Atlantic “requires the ability to detect, track and, if necessary, counter submarine threats”, which in turn demands “effective mastery of the various dimensions of combat”, Sá Granja notes. In the Arctic, where “discretion, persistence and uncertainty are decisive”, submarines are of “great operational importance” and can “expand tactical options and increase the complexity facing any potential adversary”, the Navy spokesperson adds.
Politically, Portugal has shown itself to be a “credible actor” in the defence of the alliance, with a reach that goes far beyond its immediate area and extends to “geographical spaces far from its mainland territory but directly linked to the security of the Atlantic”.
ArpãoArpão
“At a time when NATO is stepping up its focus on the High North, countries that have already demonstrated real capability to operate in that environment become particularly valuable partners,” Sá Granja says, making it clear that the “strategic relevance” of a country the size of Portugal lies not only in the “scale of its assets” but also in its “ability to offer distinct skills that are useful to the Alliance”.
The Navy will continue to monitor developments in the Arctic and is “ready, should it be asked, to contribute again in similar scenarios”, especially in the NATO framework.