Covert cat-and-mouse beneath the waves

Trump's Greenland gambit has left many confused. Why is he being so aggressive? Perhaps what remains unsaid, and unseen, is of even greater importance.

The single most important duty of the Canadian government is to protect and defend our national sovereignty. There are new and disturbing reports of American nuclear submarines passing though Canadian waters without obtaining the permission of, or even notifying, the Canadian government.
—Stephen Harper, former Prime Minister

President Trump continues to ramp up his bellicose rhetoric regarding Greenland, claiming that the US “needs that country” for its national security. There are rumours that a US Airborne Brigade, one trained in Arctic combat, is preparing to deploy to the country.

But beneath the waves, the US may already be acting to establish covert control over Greenland’s territorial waters. And not only Greenland. What do the Arctic, Atlantic, Baltic and North Seas all have in common?

Their waters are historical hotbeds of undersea activity. First in WWI, then WWII, then the Cold War and, more recently, the war in Ukraine.

One of the first British acts of WWI was to cut the undersea communications cables linking Germany with other countries. During both WWI and II, warships and merchantmen were repeatedly attacked and sunk by submarines.

For decades, NATO and Soviet subs played a constant game of undersea cat-and-mouse throughout northern hemisphere waters. At the height of the Cold War, the nuclear-powered USS Nautilus famously blasted through the Arctic ice sheet to surface at the North Pole: point-blank range for its missiles aimed at Soviet targets.

More recently, there have been multiple reports of damaged undersea cables and other infrastructure in the Baltic and North Seas. Russia is suspected, although the Chinese may also have been involved.

In late 2024, cables connecting Germany to Finland and Sweden to Lithuania were cut or at least partially damaged while a Chinese bulk carrier was in the area, among other commercial vessels.

As we also know, the Nord Stream gas pipelines running from Russia to Germany were blown up in 2022. No one has claimed responsibility. Following multiple investigations by multiple countries, including Sweden, in who’s territorial waters the incident took place, there is still no official confirmation of who did it.

Russia was initially suspected by the US and other NATO countries but no hard evidence has ever been made public to confirm this. The Swedes have now formally concluded their investigation as “inconclusive”.

Cold War antics under the Baltic

The Baltic has long been an undersea theatre of covert operations. It is one of the most economically-important seas in the world. It is also quite shallow, in places narrow and with multiple chokepoints, such as between Denmark and Sweden.

All this makes it a challenging sea under which to operate covertly. Yet that is just what the Soviet Union and NATO-member countries attempted to do throughout the Cold War.

Although Sweden and Finland joined NATO following the outbreak of hostilities in Ukraine, they were both officially neutral countries during the Cold War. (Finland was de facto in the Soviet orbit as they did not follow an independent foreign policy in the way that Sweden officially did.)

NATO’s only direct access to the Baltic was via Denmark, as Germany was divided, the eastern part belonging to the Warsaw Pact along with Poland. The three Baltic States were oblasts of the USSR.

The Baltic was thus largely a “Soviet lake”, yet one in which NATO sought some ability to operate. This they did, mostly covertly, under the waves, keeping an eye on Soviet naval manoeuvres, among other things.

In the event of conflict, NATO wanted the ability to at least partially, if not completely, deny the USSR’s use of the Baltic. The best way to do that was with a handful of submarines.

But that was easier said than done. As previously mentioned, the Baltic Sea is relatively shallow, with an average depth of less than 100 meters, and is characterized by narrow chokepoints. Notably, one of these chokepoints lies between NATO-member Denmark and neutral Sweden, whose coastline is the longest of any Baltic country.

In order to maintain strict neutrality, Sweden could not officially allow NATO submarines to operate in its territorial waters. Yet they did. In one of the most bombshell declassifications in Swedish history, in 1994 the government admitted that, during the Cold War, Sweden secretly allowed NATO submarines to operate in its territorial waters.

How that arrangement came about was also declassified and perhaps even more controversial. After the Second World War and the dawn of the Cold War, neutral Sweden concluded that the only credible way to defend itself against the USSR—particularly in the event of a NATO-Soviet conflict, in which the Soviets might seek to traverse Swedish territory to reach strategically vital Norway—was to develop its own nuclear weapons.

Yes, that’s right: peaceful, progressive, neutral Sweden sought to become a nuclear power in the 1950s, a secret the public would not learn until decades later.

Officially neutral, unofficially biased

The nuclear project was abandoned in the 1960s, in part due to the difficulty of keeping the large financial burden secret. Developing and maintaining a nuclear weapons programme is expensive. But it was also due to the fact that high-ranking Swedish intelligence and defence contacts with NATO had evolved during the post-war years.

While officially neutral throughout the Cold War, there were in fact a handful of secret agreements signed between “neutral” Sweden and NATO. These included NATO extending its nuclear deterrent umbrella to include Sweden.

As part of the deal, Sweden allowed NATO submarines to operate in its territorial waters and secretly move in and out of the Baltic. But this was not known by the public and it was also not shared with most active military personnel.

That’s how secret it was.

As long as any NATO submarines didn’t come into direct contact with the Swedish defence forces, all was well and good. But of course, as a modern country with a modern military, Sweden had substantial capabilities in place to help them detect and defend against subs operating in their waters.

You can probably guess where this is going…

From time to time the Swedish defence forces would detect a “Soviet” sub. They’d chase it and, in some cases, prepare to engage it, only for the sub to prove too elusive and escape. And each and every time, without doubt, the Swedish press would report that a “Soviet” sub had been successfully chased out of Swedish territorial waters by their defence forces.

This had the effect of both frightening and angering the public. Support for ending Swedish neutrality and joining NATO increased from the single digits to 40 percent. But it was never supported by a majority. Sweden remained officially neutral throughout the Cold War and, indeed, until 2022.

The undersea Cold War turns hot

But there was an incident in 1982 when a “Soviet” sub ended up being detected in a narrow channel, one close to the Swedish naval base at Musko and close to where defensive underwater mines had been laid.

Swedish sonar operators monitoring the area heard an explosion. Helicopter crews soon spotted a yellow dye blotch on the surface, a distress signal used by NATO-member submarine fleets.

The defence forces attempted to contact the presumably-damaged sub, using international frequencies and multiple languages, ordering the sub to the surface.

While the sonar operators heard clear signs of activity on the sub, the radio operators received no response to the order. They then prepared to drop depth charges to finish off the sub, still considered a danger. But at the last moment they received an order from the Swedish High Command: They were to stand down and permit the damaged “Soviet” sub to escape.

Several members of the defence forces involved in the operation raised objections, escalating their concerns up the chain of command and even bringing the issue before the Defence Committee of the Swedish Parliament. The Committee opened an official investigation.

One month later, with the investigation ongoing, Caspar Weinberger, the US Defence Secretary, visited Sweden, the first ever to do so. Several months later, as would also be the case with the more recent Nord Stream incident, the investigation was inconclusively closed. Some records were subsequently destroyed.

(If you’ve never heard of the above, admittedly obscure events, there is a Cold War submarine operations documentary available on YouTube that goes through these and other curious underwater incidents of the era. You can find it here.)

Former Swedish Prime Minister Olof Palme, a vocal advocate for neutrality and a strong, independent defence force, saw his popularity wane as a result of the incident. Despite this decline, he remained in office until February 1986, when he was tragically assassinated on a dark street in Stockholm late one evening.

He was the first Swedish political figure to be assassinated since King Gustav III in 1792. The assailant escaped. The crime remains unsolved to this day.