The world's largest satellite ground station, on the Svalbard archipelago off Norway, is used by Western space agencies to gather vital signals from polar-orbiting satellites. This January, one of two fibre-optic cables on the Arctic seabed connecting Svalbard to the mainland was severed. Norway was forced to rely on a back-up link.
In April 2021, another cable – one used by a Norwegian research laboratory to monitor activity on the Arctic seafloor – was ripped away.
"This could have happened by accident," Norway's defence chief Eirik Kristoffersen told Reuters in response to the ruptures, which received little media coverage outside Norway. "But the Russians are capable of cutting cables."
He was speaking generally and did not offer any evidence to suggest deliberate damage, but months later, in September, saboteurs caused major leaks to suddenly erupt in gas pipelines from Russia to Europe on the floor of the Baltic Sea. Russia's defence ministry did not respond to a request for comment.
As Russia's invasion of Ukraine ends a post-Cold War era of low tension and cooperation, such events highlight how hard it is for states to monitor their own waters – particularly in the Arctic, an ocean one and a half times the size of the United States, where satellites are crucial to allow real-time detection and monitoring of activity.
Over recent years, NATO allies and Russia have scaled up military exercises in the region; Chinese and Russian warships conducted a joint exercise in the Bering Sea in September. Norway raised its military alert level in October.
But the West trails Russia in military presence.
Since 2005, Russia has reopened tens of Arctic Soviet-era military bases, modernised its navy, and developed new hypersonic missiles designed to evade U.S. sensors and defences.
Four Arctic experts say it would take the West at least 10 years to catch up with Russia's military in the region, if it chose to do so.
"The Arctic is currently a dark area on the map," said Ketil Olsen, formerly Norway's military representative in NATO and the European Union, who heads Andoeya Space, a Norwegian state-controlled company that tests new military and surveillance technologies and launches research rockets.
"It's so vast and with few civilian surveillance resources."
The chief of the U.S. Northern Command, General Glen VanHerck, told a Senate hearing in March the United States needed better Arctic "domain awareness" to detect and address Russian and Chinese capabilities to launch advanced missiles and destroy communications infrastructure. In a Pentagon strategy document released in October, the United States committed to improving early warning and surveillance systems in the Arctic, but the pace of the planned modernisation is unclear.
At the same time, fast-rising temperatures are creating problems for some U.S. military infrastructure built on permafrost foundations, which are melting. Coastal erosion could also impact U.S. radar sites, the Pentagon says.
There are few risks in the near term, U.S. officials and military analysts say: The West is far stronger than Russia in conventional forces and Russia's limited success in Ukraine exposed weaknesses many in the West had not expected.
Russia's military efforts are currently mostly focused on Ukraine, leaving "very limited strength of personnel on the army side" in the Arctic Kola Peninsula, which is home to its Northern Fleet navy and nuclear submarines, according to Kristoffersen.
U.S. missile defences are designed to defend against a limited attack from a rogue state, and the United States has expressed confidence in its ability to deter a nuclear attack by Russia or China. But insufficient visibility in the Arctic could limit U.S. response time in a crisis, a situation VanHerck and other officials want to avoid.
"What you can't see and what you can't determine, you can't defend from," VanHerck told the Senate.
Police investigating the Norwegian cable ruptures interviewed the crew of Russian fishing trawlers that had been nearby, but dropped the investigations without charge for lack of evidence of what happened; the government said it brought forward a planned upgrade of the back-up line.
If a sabotage attack were to happen in Norway, it would likely be difficult to hold anyone accountable for it, Hedvig Moe, deputy head of Norway's PST police security service, told Reuters. "We call it a deniable attack in our world," she said.
"NATO is increasing its presence in the Arctic with more modern capabilities," NATO chief Jens Stoltenberg told Reuters. "This is of course a response to what Russia is doing. They have significantly increased their presence ... and therefore we also need greater presence."
As a shrinking ice cap opens up new sea lanes and resources, the Arctic is becoming strategically more important. Parts are accessible in a few months in summers as the sea ice melts, unlocking opportunities.
For Russia, vast oil and gas resources lie in its Arctic regions, including a liquefied natural gas plant on the Yamal Peninsula.
The waters between Greenland, Iceland and the UK - known as the GIUK Gap - are the only way Russia's northern-based ships can reach the Atlantic. The shortest path by air to North America for Russian missiles or bombers would be over the North Pole.
For the NATO allies, the GIUK Gap is crucial for links across the North Atlantic. There are oil and gas fields too: Norway is now Europe's largest gas supplier.
If Sweden and Finland join the Alliance, seven out of eight Arctic countries will be members.
Also at risk today are communications cables and satellite systems including the global positioning system (GPS) linking both civilian and military users, Andrew Lewis, former commander of NATO's Joint Task Force in Norfolk, Virginia, told Reuters.
In July, President Vladimir Putin launched a new naval strategy pledging to protect Arctic waters "by all means."
Russia usually tests its nuclear deterrent in the Arctic in the autumn. This year, that happened on Feb. 19, five days before its Ukraine invasion.
"This was of course a signal," said Norway's defence chief Kristoffersen.
Diplomacy in the region was thrown into disarray in March when seven members of the Arctic Council, a forum for international cooperation, said they would boycott talks in Russia, which currently holds the body's chairmanship.
An incident on Oct. 15 underlined the sharpening tone. In a speech at an Arctic forum in Iceland, the chairman of NATO's military committee, Rob Bauer, criticised China for not condemning Russia's invasion of Ukraine. China calls itself a near-Arctic state and Beijing's envoy to Reykjavik, He Rulong, was in the audience.
He stood up and said Bauer's speech was "full of arrogance" and "paranoid," accusing him of heightening tensions. NATO and the Chinese embassy in Iceland declined to comment on the exchange.
"At the moment, the military balance in the Arctic is heavily weighted towards Russia," said Colin Wall, research associate at Center for Strategic and International Studies in Washington.
Russia's bases inside the Arctic Circle outnumber NATO's by about a third, according to data compiled by the International Institute for Strategic Studies (IISS) and Reuters.
Russia now has 11 submarines capable of launching long-range nuclear weapons for use in an all-out nuclear war, eight of them based in the Arctic Kola Peninsula, according to the IISS. NATO has 22 between the United States, France and the UK.
In July, Russia's navy took delivery of a new submarine, Belgorod, which can carry the Poseidon torpedo, a new, nuclear-armed stealth torpedo designed to sneak past coastal defences by travelling along the seafloor. Russian state media have said Poseidon could cause a giant tsunami that would turn the coastline into a "radioactive desert."
Moscow also has over the last two years tested a hypersonic glide missile, Zircon, which Putin said in 2019 can reach nine times the speed of sound, making it the world's fastest. In February, it said the missile was launched in the Arctic waters between mainland Norway and Svalbard.
"We are starting serial production of Zircon missiles, and we have actually put it into service," Defence Minister Sergei Shoigu was quoted as saying by military news outlet Zvezda on Aug. 20. Russia's defence ministry did not respond to a request for more details.
Russia's icebreaker fleet vastly outnumbers those of other nations, according to the IISS. Official data shows it has seven nuclear-powered icebreakers and around 30 diesel-powered ones. The United States and China each have two diesel-powered icebreakers in operation.
For decades, Arctic NATO allies stuck to a belief that conflicts with Russia would not spill over into their region: With overall defence budgets capped, investments in military hardware and surveillance and communication capabilities were often considered too expensive.
Now NATO and Arctic allies are changing their stance.
Since Russia launched its "special operation" in Ukraine, Canada has pledged to boost military spending by some C$13 billion ($10 billion) including an upgrade of an early warning radar system with the United States, the North American Aerospace Defense Command, or NORAD, and new surveillance planes capable of detecting submarines.
The first planes will be delivered in 2032. Given the challenges of the harsh environment, it will take decades to be ready, Canada's Chief of Defense Staff General Wayne Eyre told a parliamentary committee in October.
Eyre says one reason NORAD's research and development component needs modernising is to track hypersonic missiles better.
"That is of great concern – the ability to detect hypersonics coming from any country – and we've seen some technological advances from some of the competitors out there," Eyre told reporters in November.
He said it was difficult to judge the effectiveness of Russia's hypersonic missiles based on those used in Ukraine, because the distances in Ukraine were far shorter than any that could be used to target North America.
Since 2020 a joint force command in Norfolk, Virginia in the United States has been monitoring the Atlantic, but the Atlantic Council, a U.S. think tank, says there are not enough satellites above the North Pole to give a complete picture. General VanHerck said in May that the military is testing some of the hundreds of polar-orbiting satellites launched in recent years by commercial providers SpaceX, owned by Elon Musk, and Britain's OneWeb.
The U.S. military says it is planning "major investment upgrades" at a U.S. base at Thule, Greenland to fix ageing infrastructure. A U.S. delegation travelled to Greenland in May to explore radar locations, a diplomatic source told Reuters.
Sweden and Finland have begun investing in surveillance and deterrence capabilities and military hardware including jets so their air forces can fight alongside Arctic NATO allies. Denmark has set aside some $200 million to improve its Arctic military capabilities, including satellites and surveillance drones capable of flying up to 40 hours, and is reopening a Cold War era radar on the Faroe Islands between the UK and Iceland.
Norway, whose maritime areas spread across 2 million sq km (770,000 square miles), has four satellites to help monitor the Arctic. It is launching four more, two in 2023 and two in 2024. It is also investing $35 million in Andoeya Space to set up a spaceport. Sweden and Canada are also planning Arctic spaceports.
Andoeya Space is a partner in an Arctic surveillance and sensing project led by U.S. aerospace company Boeing Co. Based on satellites, unmanned aircraft, drones, ships and unmanned submarines developed for the Arctic environment, the project - under development since 2018 - says it is ready to offer NATO allies real-time updates in the north, including surveillance of enemy vessels, aeroplanes and submarines.
The U.S. Department of Defense is installing a long-range radar system allowing satellites and other ground-based radars to work together in Alaska that it says will "be able to address hypersonic missiles in future configurations." It is due for completion in 2023, but the Missile Defense Agency declined to comment on whether it would be able to intercept the Zircon.
More answers may come in a stand-alone Arctic strategy document the Pentagon is expected to publish next March, a U.S. military official said, in what would be the first update since 2019. It would come as the Pentagon tries to better define what capabilities are needed for American warfighters at dangerously low temperatures.
"When it's dark all the time in the winter and it's 50- to 60-below-zero or even more, it is just brutal," the official told Reuters.
(Additional reporting by Steven Scherer in Ottawa, Mark Trevelyan in London, Phil Stewart and Idrees Ali in Washington; Edited by Sara Ledwith)