Portuguese Diesel-Electric AIP Submarine Just Patrolled Under The Arctic Ice

A conventionally powered Portuguese attack submarine has completed a rare voyage under the Arctic ice. As well as being a first-of-its-kind mission for the Portuguese Navy, the deployment underlines the growing importance of the Arctic theater to NATO’s submarine fleet. Although it’s nuclear-powered boats that traditionally dominate in this challenging area of operations, the Portuguese deployment demonstrates that conventionally powered submarines have a role to play here too.

The Portuguese Navy’s Arpão (S161) recently returned to its home base in Alfeite, Lisbon, after a 70-day deployment under NATO’s Operation Brilliant Shield. It’s unclear exactly how much time the Portuguese submarine spent navigating under the polar ice, but the broader mission was, according to NATO, “aimed at deterrence and defense of the Euro-Atlantic area.”

“We have successfully achieved our objectives of surveillance and patrol in the North Atlantic, demonstrating the capabilities of this type of conventional submarine in Arctic conditions,” said Portuguese Navy Cdr. Taveira Pinto, who commanded the submarine. “Our ability to operate across the entire spectrum of the Atlantic is a testament to our commitment to supporting the operations of the Atlantic alliance.”

Under-ice operations are by no means straightforward and for conventionally powered submarines they are notably harder. The traditional requirement to surface at regular intervals to recharge their batteries means that conventionally powered submarines — especially diesel-electric ones — are less-than-regular visitors below the Arctic ice.

While there have been under-ice experiments with conventionally powered submarines dating back to at least 1931, and some significant demonstrations, as by the USS Boarfish in 1947, conventionally powered boats have traditionally been limited to traveling among the ice floes, rather than below the ice pack. Meanwhile, the emergence of nuclear propulsion since the late 1950s means that modern under-ice operations are very much the preserve of these nuclear-powered submarines, which don’t have a requirement to surface.

The Portuguese Navy’s Arpão (S161) is part of the two-strong Tridente class, built by Howaldtswerke-Deutsche Werft (HDW) in Germany and based on the export-optimized Type 214 design. These are broadly similar to the Type 212 submarines, operated, among others, by Germany, as you can read about here.

With a submerged displacement of 2,020 tons and an armament of eight 533mm tubes for Black Shark torpedoes, the Tridente class are driven by an air-independent propulsion (AIP) system, charging their batteries using liquid oxygen and hydrogen fuel cells. You can read more about this technology here.

The Portuguese Navy’s Tridente (S160), sister boat of the Arpão (S161), at its home base of Alfeite in May 2018. Antonio da Silva Martins/Wikimedia Commons

Since the AIP system requires no fresh air for battery charging, these submarines can remain submerged longer, sometimes up to several weeks, depending on speed.

Compared to diesel-electric submarines, AIP boats like these offer better under-ice capabilities, although they still fall short of nuclear-powered ones.

There are perhaps questions about the reliability and maintenance requirements of at least some AIP systems in the brutal Arctic environment and they also are less well-suited to oceanic transits at high speeds — which would typically be required to get the submarine to the ice cap in the first place.

Then, once in the Arctic, the mission of an AIP submarine will, to a significant extent, have to be planned in advance around options for surfacing once the AIP fuels are exhausted, after which air is needed for the backup diesel engines to recharge the batteries.

Other potential difficulties when operating in this environment include the limited nature of rescue opportunities should a submarine get into trouble. While this is an issue for any submarine operating under the ice, it becomes more problematic with a conventionally powered that is not able to break through the ice. Meanwhile, navigation under the ice is notably complex, with a unique acoustic environment that has to be negotiated.

Clearly, however, these challenges were overcome and, with unspecified assistance provided by the navies of Canada, Denmark, and the United States, the Arpão successfully completed its mission.

As to what that mission consisted of, NATO described in a statement how the Arpão was tasked with monitoring non-alliance military platforms, both surface and submarines, known to operate in the Euro-Atlantic region. This would appear to be an unusually explicit confirmation of the Portuguese submarine being used to shadow and monitor Russian surface vessels and submarines.

Meanwhile, there are few details available about the scope of Operation Brilliant Shield, although a statement from the Italian embassy in Latvia said it was “aimed at patrolling the Baltic Sea and securing the energy infrastructures located in the area.” This is something that has taken on much greater resonance after the September 2022 explosions on the underwater Nord Stream gas pipelines which were built to carry Russian natural gas to Germany, via the Baltic. The source of the apparent sabotage so far remains a mystery.

However, it was the presence of the Arpão in the Arctic region that was the standout aspect of the submarine’s latest deployment.

Even before Russia’s full-scale invasion of Ukraine and the further ramping up of tensions between NATO and Moscow, submarine operations under the Arctic ice were seeing a resurgence of interest.

Amid the growing geopolitical competition in this highly strategic region, Russian Navy and NATO submarines have stepped up their activities here, including some high-profile events involving nuclear-powered boats.

In March 2021, for example, Russia released details — as well as the video below — about the submarine activity during its Umka-2021 drills, which included three Russian ballistic missile submarines surfacing next to each other from beneath the ice near the North Pole, as you can read about here. The same exercise saw an unspecified Russian nuclear submarine fire a torpedo underneath the Arctic ice, perhaps using this weapon to blast a hole in the Arctic ice to allow the submarines to raise their conning towers above the ice. At the same time, MiG-31 Foxhound interceptors flew over the North Pole and troops conducted maneuvers on the ground in extreme cold weather conditions.

Exercises like this reflect the growing significance of the Arctic region to Russia, on both military and economic levels.

For Russian ballistic missile submarines, the Arctic ice is critical to survival, or at least making it that much harder for NATO forces to track their movements. More generally, the Arctic region has historically been an ideal place for submarines from various countries to operate discreetly.

In its statement about the Portuguese submarine’s deployment, NATO also points to the particular threat posed by Russian submarines and the importance of its own anti-submarine warfare (ASW) capabilities as a counter to a force that is adding increasingly advanced designs.

“In the realm of ASW, NATO submarines play a crucial role in protecting allied shipping lanes and ensuring the security of maritime supply routes. The ongoing threat from adversarial submarines, particularly from Russia, necessitates robust ASW capabilities. NATO submarines regularly team up with maritime patrol aircraft and surface ships to hunt for enemy vessels with very little information. NATO’s submarines, equipped with advanced sonar systems and ASW weaponry, are at the forefront of countering these threats, ensuring the safety and security of critical maritime infrastructure.”

The U.S. Navy, too, has notably stepped up its submarine operations in and around the Arctic region, at least in terms of public signaling about these activities.

An example of this came in August 2020, when the Pentagon took the rare decision to publicize a visit to Norway by the highly advanced and extremely secretive submarine USS Seawolf.

USS Seawolf on the surface in a fjord near Tromsø, Norway on August 21, 2020. U.S. Navy

The Seawolf and its two sister boats, including the larger and uniquely configured spy submarine USS Jimmy Carter, are considered particularly well suited to cruising quietly under the Arctic ice.

Up until now, operations under ice have been most widely associated with nuclear-powered submarines, but the debut voyage by the Portuguese Navy’s Arpão in these waters suggests that we may see other conventionally powered NATO boats conduct similar missions.

As NATO said in a statement related to the Portuguese mission, “The strength of NATO’s submarine force lies in multinational collaboration … NATO’s submarine fleet significantly reinforces the alliance’s strategic and tactical advantage while patrolling the Atlantic and High North, the Baltics, and the Mediterranean Sea, and remains pivotal to the defense of the alliance.”

Clearly, nuclear-powered submarines will remain the prime arbiters of underwater warfare below the ice, although the ever-increasing strategic significance of the Arctic means that there is growing scope for conventionally powered boats to contribute to these operations as well.

With tensions between NATO and Russia at a high, this is also being reflected in the competition for untapped natural resources the Arctic, where climate change is leading to the emergence of new economic opportunities that various powers are keen to exploit.

As Russia and the United States work to expand their abilities to project military power into the Arctic, NATO’s submarine fleet — in all its diversity — will likely also take on an expanded role in this area of operations.

Contact the author: thomas@thewarzone.com