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 began to be monitored by satellites in 1978, has beenretreating significantly in recent decades. On 22 March, after the end of winter, the period of greatest accumulation, the maximum extent for 2026 was reached - 14.33 million square kilometres, according to the US National Snow and Ice Data Centre (NSIDC). This is the lowest peak since records began, and the second year in a row.
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With this region warming almost four times faster than the rest of the planet, new maritime routes and business opportunities are opening up for many countries that have had their eye on the Earth's far north for centuries, fascinated by its isolation and climatic conditions, which are fertile for scientific research, but above all by the natural wealth deposited there, from oil and gas to strategic minerals.
The latest report from the Arctic Council (source in Portuguese) shows a 40 per cent increase in the number of unique ships operating in the area over the last 12 years, and the distance travelled has soared by 95 per cent, from 6.1 million to 11.9 million nautical miles. It should be noted that these figures include vessels from the eight Arctic states (United States, Canada, Iceland, Norway, Sweden, Finland, Denmark and Russia) and also those that frequently enter the area delimited by this Polar Code under the flag of the Arctic Council Observer States.
Although the melting of ice caused by climate change is making incursions into the region more inviting for military, cargo and cruise ships, navigation at high latitudes is far from peaceful. "In many ways, 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.
In addition to the challenges posed by the intensification of maritime traffic, global warming is making the ice thinner, leading to an increase in glacier fragmentation and the formation of more icebergs. Even summer days are problematic: this is when melting is accentuated by the higher temperatures.
Ice sheets drifting in the water are unpredictable, and when they collide, pushed by winds or ocean currents, they accumulate, which causes them to evolve into a kind of "mountain range" on the surface ("ridges") and also underwater ("keels"), and the underwater formations can reach tens of metres. This is one of the main dangers for those on submarine missions in the Arctic Ocean. If the submersible is conventional, and therefore has limited immersion autonomy, the risk is greater because, in areas of dense cover, it will be impossible or much more difficult to surface.
There is also the threat of floods or, more often, fires. In a report for The War Zone (source in Portuguese), a website specialising in defence issues, Eric Moreno, a veteran of the US Navy and a submariner between 2001 and 2008, explains that the more space the submarine has, "the greater the atmosphere available to 'absorb' a fire", which gives the crew "more time to react appropriately". Conversely, the expert points out, the room for manoeuvre is narrower in a traditional submarine, which, because it is smaller and has little headroom, is prone to a faster build-up of heat and smoke, exacerbating the difficulties of responding to an emergency.
Because it is a theatre of operations with extreme conditions, navigation under the ice in the Arctic has, since the late 1950s, been reserved for nuclear submersibles, most of which are over 100 metres long, with high speed and practically unrestricted autonomy. The Portuguese Navy, however, overcame all fears, including those of NATO allies, and, between April and June 2024, took the NRP Arpão to the depths of these glacial waters, becoming the first to do so with a conventional submarine in recent history.
The garrison, made up of three dozen members and commanded by frigate captain Taveira Pinto, stayed under the ice sheet in the Greenland area for an aggregate of four days, in an unprecedented mission, both for its operational mastery and for breaking down borders that were thought to be insurmountable. Portugal thus joined the US, UK and Russia in a restricted range of countries that have already operated under the polar ice cap, with these powers having the advantage of nuclear reactor-powered submarines.
"Own operational expertise"
The NRP Arpão left the Lisbon Naval Base on 3 April 2024, as part of NATO's Operation Brilliant Shield, for a 78-day mission, supported by the US, Canadian and Danish navies, which included several stages, with a total of 1,800 hours of sailing, 1,500 of which were immersed.
At the end of the first 22-day patrol, which was used to test the new procedures and changes made, the vessel docked in the port of Nuuk, Greenland, where it refuelled with fuel and food. The voyage then continued north, passing through the 66º33'N parallel, which marks the border of the Arctic Circle, with the then Chief of the Navy's General Staff, Henrique Gouveia e Melo, on board , who had masterminded this expedition more than a decade ago.
After 39 hours and 30 minutes of deep immersion under the ice, they proceeded to explore the plate, which involved making natural openings for a hypothetical emergency ascent, as well as monitoring the width and density of the frozen cover.
This feat by the Portuguese sailors was supported by the Arpão's Air IndependentPropulsion ( AIP) technology - a fuel cell system which, being equipped with hydrogen and oxygen tanks, does not require fresh air to charge the batteries, ensuring energy production underwater, which allows these diesel-electric or conventional submarines to considerably extend their submergence time, up to two or three weeks, depending on speed, making patrols under the ice possible.
The confidence for this mission therefore came from the "rigorous technical assessment that the platform had intrinsic characteristics compatible with this type of environment [the Arctic]," the Portuguese Navy explained to Euronews. But this endeavour would not have been a success without "demanding preparation" over seven months, through "in-depth study of the area" and "concrete material adaptations" after reviewing the ship's systems.
In the official documentary about this experience, Gouveia e Melo reports that the Arpão's garrison came across "mountains" of ice that extended "ninety metres down" from the surface. These obstacles are part of what the Navy describes as a "complex combination of challenges", from "fixed ice, loose ice, icebergs" to "acoustic conditions very different from those of the open sea" and the "severe limitation of options in the event of an on-board emergency".
One of the risk mitigation measures was the installation of a high-frequency sonar, with support from the Hydrographic Institute (source in Portuguese), as well as specific sensors, in order to detect ice, measure its thickness and reinforce navigation safety. Arsenal do Alfeite S.A. also designed and fitted protection to the tower to prevent the most sensitive masts, namely the periscope and the optronic mast, from colliding directly with ice sheets.
Recalling that "sensors, engineering, training and doctrine were adjusted for a very specific and segregated theatre", the Navy says it has shown the allies that "the Portuguese submarine capacity is technologically mature, capable of learning quickly and adapting (...) in highly complex environments".
The US_Ice Pilots_ provided "initial guidance", but it was the Portuguese who, "to a large extent", ensured the study of the region, the preparation of emergency situations, the training of the garrison and the tactical use of the submarine's sensors, stresses the Navy, which "reveals the national capacity to analyse meteorological and oceanographic data, absorb allied knowledge and transform it into their own operational competence".
Where no Western submarine has ventured since the Second World War
The immersion navigation, at a depth that allows the masts to be positioned above the waterline (periscopic quota), in the so-called Marginal Ice Zone (MIZ), further emphasised the merits of the Portuguese mission.
It was a manoeuvre that caused general astonishment among the allies, confesses commander Taveira Pinto, in the official documentary, choosing it as the highlight of the operation. The MIZ is the confluence zone between the rigid ice sheet and the open waters, where, due to exposure to violent storms and giant waves, the ice floes break up more quickly and take on unpredictable trajectories.
Since the Second World War, the Navy stresses, no other Western submarine has dared to operate in this "highly problematic" and "uncertain" area, where "both detection and manoeuvre are made more complex" by "fragmented ice, variable-sized plates, very high environmental noise and the presence of marine life, which degrades the normal use of sonar as the main safety sensor".
Using the instruments in this chaotic context is a particularly sensitive task, not least because of the "associated physical risk". The ice sheets found in this location can be large enough to cause structural damage if they come into contact with the vessel.
"That's why the technique developed by the NRP Arpão to return to the periscopic quota made the difference and made it possible to transform a traditionally avoided area into a space where it became possible to operate with acceptable safety," the Navy maintains, emphasising that this exercise provided "freedom of action" and made submarine operations in the Arctic more flexible.
More than proving that it can operate in an icy ocean, the Harpoon brought "tactical innovation in a real environment", with "adaptability" to a "theatrein which access, survival and discretion depend on very fine decisions". In this way, Portugal "produced operationally relevant knowledge for the allies", embodied in an Arctic navigation manual - a comprehensive basis that facilitates the work of anyone who decides to launch incursions into this region in the future.
After breaking new ground and risking taking steps that were not backed up by means and technology designed from scratch to meet the demands of the tasks assigned, Portugal systematised its knowledge in what the Navy presents as a "doctrine tool", which illustrates lessons learned from real experience.
In this publication, different variables are explored in depth, such as multidisciplinary preparation, interpreting acoustic behaviour in a scenario that the Portuguese were not used to, assessing ice and adapting safety procedures.
These lessons are being taken into account by Canada, Portugal's NATO ally, in order to make the necessary adjustments to its new submarine fleet and ensure their suitability for operations in the Canadian Arctic, which covers 40 per cent of the country's territory and more than 70 per cent of its coastline.
The adaptation of the Harpoon as a reference
"What struck me most was the way the crew of the NRP Arpão and the Portuguese Navy approached the mission. They were calm, professional and thoroughly prepared," Harrison Nguyen-Huynh, commander of the Canadian Navy, who was on board the Arpão throughout the 2024 operation as liaison officer to support the garrison, told Euronews.
Praising the attitude and spirit of cooperation of the Portuguese submariners, Commander Nguyen emphasised that this NATO exercise was another important opportunity to collaborate with allies, "in order to gain insight into some of the challenges of operating in the North".
Observing the Harpoon in "operations near, on and under the ice", adds the Deputy Commander of Canada's Submarine Force, will help Ottawa modernise its submersibles, especially since "one of the main requirements" of the current acquisition programme is the "ability to operate in the Arctic environment".
The project was launched in 2021 with the aim of studying operational environments and then defining the characteristics and technology of the Canadian Navy's future submarines, which will replace the current fleet (four vessels), belonging to the Victoria class, acquired second-hand from the UK in 1998 and scheduled to leave service at the end of the 2030s.
Canada's former prime minister, Justin Trudeau, has not ruled out the possibility of nuclear propulsion, something that the country's defence authorities would ultimately reject because of the substantially 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 autonomy that will provide discretion, persistence and lethality as key capabilities". Canada, which has the longest coastline in the world - 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 executive added.
Even if conventional submarines are involved, a gamble of this scale and ambition requires opening the purse strings. Estimates point to 60 billion dollars (around 51 billion euros), although defence analysts have already predicted a total cost of around 100 billion dollars (close to 85 billion euros), reports the Canadian newspaper Ottawa Citizen (source in Portuguese).
According to the same publication, this could be the biggest military acquisition ever in Canadian history. The government wants to speed up the process and the contract could be signed this year, but the Canadian Navy estimated back in 2025 that the first submarine would not be fully operational until 2037.
The new submersibles won't arrive with all the capabilities for navigating under the Arctic ice, revealed Canadian Navy Vice Admiral Angus Topshee, quoted by The Globe and Mail. This is where Portugal's example comes in: the modifications and additions made to the Harpoon will guide the refitting work that will be undertaken after delivery, both in terms of the structure and specialised equipment.
As Commander Nguyen said in an interview with Euronews, safety is one of the priorities. The installation of protection to shelter the masts and increase the strength of the towers, one of the main adaptations carried out by the Portuguese, is therefore a requirement to avoid structural damage and to take precautions in the event of an emergency scenario involving breaking through the ice.
Another fundamental aspect, says Nguyen, is efficiency, largely guaranteed in the case of the 2024 mission by the specialised sonar at the top of the tower, which was useful for mapping the ice above and detecting open water. Operations in the Arctic require a two-dimensional view (top and bottom) and the Harpoon, by incorporating this extra valence that allowed it to monitor the glacial "ceiling", gave it a more refined maritime situational awareness.
For future Arctic missions with diesel-electric submarines, the Portuguese experience provides important guidelines for conducting static manoeuvres and understanding the specificities of the marginal zone, where the noise produced by the movement of the ice affects the performance of the sensors. The mixing of fresh and salt water can also influence the transmission and analysis of sound, points out the Canadian Association for NATO. (source in Portuguese) The recordings made by the Portuguese will therefore be an important support resource so that, for example, false echoes close to the ice can be recognised and detection improved.
The Navy told Euronews that the results obtained by Arpão were "very positively received" by the 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 capacity and increases the effectiveness of our operations," says Commander Nguyen, emphasising that Canada, as an "Arctic nation", sees campaigns in the "North" as "essential" to protecting its sovereignty.
Conventional submarines as a means of combat under the ice
At the moment, there are no plans for new missions by Portuguese submarines in the Arctic, "due to other operational and strategic priorities", says Ricardo Sá Granja, spokesman for the Navy, in an interview with Euronews. Nevertheless, Portugal remains attentive to what happens in this region, "where geopolitical disputes are intensifying".
The Arctic is, in fact, becoming increasingly militarised. Russia has one of the largest concentrations of nuclear weapons in the world on its Kola Peninsula, which borders Norway and Finland, and operates submarines in these waters that can carry dozens of warheads each.
There has even been an increase in the Russian submarine presence near the GIUK passage, a strategic point in the North Atlantic between Greenland, Iceland and the United Kingdom, of crucial importance for access to Atlantic waters from the Arctic. According to NATO commanders, Cold War levels of activity may have been surpassed here.
As for China, in 2018 it proclaimed itself a "quasi-Arctic state" and continues to invest in the "Polar Silk Road", a plan that consists of creating new maritime trade routes through the Arctic Ocean in order to reduce the journey time between Asia and Europe to 18 days.
Faced with this escalation and greed, the Portuguese Navy says it is committed to the "collective effort that contributes to the stability" of the far north, but stresses that**"deterrence and defence of the Euro-Atlantic area are not done in the abstract".**
What the mission carried out by the Arpão also demonstrates is that Portugal and other countries with smaller military budgets, despite the restrictions of conventional submarines, have the potential to play a more active role in underwater combat, including under the ice.
If, on the one hand, these vessels are limited by their lower speed and shorter submergence times, they can, on the other hand, remain silent when powered by batteries. This discretion is an advantage that could be exploited, in the current context of greater hostility, in surveillance, intelligence and other operations.
Operating in the North Atlantic "requires the ability to detect, track and, if necessary, counter submarine threats", which is realised in the "effective mastery of the various dimensions of combat", Sá Granja stresses. In the Arctic, where "discretion, persistence and uncertainty are decisive", conventional submarines have "great operational relevance" and can "broaden tactical options and increase complexity for any potential adversary", adds the Navy spokesman.
From a political point of view, Portugal has proven to be a "credible actor" in the defence of the alliance, with a radius of action that goesfar beyond its immediate area, reaching**"geographical spaces far from its continental territory, but directly linked to the security of the Atlantic".**
**"**At a time when NATO is stepping up its attention to the High North, countries that have already proven their ability to operate in this environment become particularly valuable partners," says Sá Granja, making it clear that the "strategic relevance" of a country the size of Portugal lies not only in its "scale of resources", but also in its "ability to offer differentiated and useful competences to the Alliance".
The Navy will continue to monitor developments in the Arctic and is "prepared, if requested, to contribute again in similar scenarios", especially within NATO.