A mysterious incident occurs. It can’t be conclusively attributed, but the targeted country pins the attack with near-certainty on another country — which unleashes a disinformation campaign, ridiculing the target and proposing a range of other explanations. The UK in 2018? Yes – and Sweden, for far longer. Over the past several decades of hunting submarines in its waters, Stockholm has dealt with similar combinations of mysterious-incident-plus-disinformation-campaign. Other Western nations would do well to learn from the Swedes’ experience.

On Oct. 16, 2014, news broke that Sweden’s signals intelligence agency, the National Defence Radio Establishment, had intercepted traffic on a Russian emergency channel. The following day, a resident of the Stockholm archipelago contacted the Swedish Armed Forces, saying he had seen what looked like a submarine. The armed forces immediately dispatched its sub-hunting flotilla and several other vessels. Later that evening, the signals intelligence agency intercepted encrypted Russian radio traffic, tracing its source to an area within the archipelago.

Three days later, the Swedes still hadn’t found the suspected submarine. The Russian defence ministry denied that any of its subs were in Swedish waters, suggesting instead via Russian news outlets that it must be a Dutch vessel. Other Russian news outlets submitted that the Swedish Navy had mistaken an animal for an underwater vessel. Then Russian media began referring to the suspected U-boat as Sweden’s “phantom submarine.” When the hunt was disbanded without a submarine having been found, the Russians seemed right.

“The Russian tactic is to put on a blank face and sow uncertainty among everyone who doesn’t have 100-percent-certain evidence,” explained retired Gen. Sverker Göranson. “And the Russians always try to make the other side look like idiots. As soon as the suggestion appeared that the detected sound might come from an animal, the Russians picked it up in order to ridicule us.”

As Sweden’s chief of defense until 2015, Göranson had ultimate responsibility for the 2014 submarine hunt, and as a result became a particular target of Russian mockery. “Russian media found a video snippet of me in yellow rain boots dancing to an ABBA song that they showed over and over,” he recalled. “Their message to the Swedish public was, ‘the person in charge in your country is a clown whom you can’t trust.’ They were ridiculing those in charge at all levels.”

This pattern of denial and ridicule is familiar to the Swedish armed forces, which have for decades hunted suspected submarines near the 2,700-kilometer coastline surrounding the mainland and the island of Gotland. Hunting submarines is like documenting nerve gas attacks, but much harder. Submarines, especially the mini-submarines often used by the Russian Navy, can easily hide and escape in shallow archipelagic waters.

On Oct. 27, 1981, there was no denying that a Soviet sub was in Swedish territory; it had run aground in a military zone in the archipelago off the southern city of Karlskrona. As a standoff ensued between Stockholm and Moscow about what to do about the sub and its crew, the event grew into international news. But even with such an embarrassment on their hands, the Soviets conducted a brilliant disinformation campaign. The sub’s captain said the crew had lost their bearings after all their navigational instruments failed– but when tested by the Swedes, the instruments worked fine. “Anyone a bit critical to the official Swedish story could find a story that fitted their convictions,” said Joakim von Braun, an independent Swedish defense analyst who specializes in Russian intelligence and naval operations. “The Soviets offered had a real smorgasbord of rumors and disinformation.” Soon Swedish public opinion was divided about whether the submarine had intentionally or unintentionally ventured into a Swedish military zone.

The following year, the Swedish Navy failed to catch a suspected Soviet submarine off the coast of Stockholm. “We found traces of tracks on the seabed, but the Soviets said they didn’t have any submarines that left such marks,” noted retired Commodore Nils-Ove Jansson, who commanded several submarine hunts in the 1980s and subsequently served as deputy director of the country’s military intelligence agency. “Then they said it must be a NATO submarine. Their alternative explanations created doubt among the Swedish public and led to a situation where many Swedes thought we were making up the submarine hunts in order to get more money.”

Such messages work on multiple levels. “At one level the Russians send the message saying, ‘Look at what we can do,’ but then they deny it,” said the Royal Navy’s Vice Adm. Sir Anthony Dymock, a former UK Permanent Military Representative to NATO.

To this day, the Swedish public remains divided as to whether the submarine intrusions actually took place. One active group of doubters, the Medborgargruppen, advances the idea that the intrusions exist only in Swedish officers’ imagination.

This all echoes what the UK has experienced since Sergey and Yulia Skripal were poisoned last month. Russian government representatives have suggested that the nerve gas came from Sweden, the Czech Republic, or even Britain’s own military lab. Though social media is new, information warfare most certainly is not. “What we’re seeing today, with trolling of decision-makers, is just a repetition of what we [the Swedish armed forces] were subjected to,” Jansson said.

Indeed, the Swedes’ long experience with Salisbury-like combinations of attacks and disinformation campaigns has given them expertise that other countries can learn from. “Don’t respond to disinformation,” Göranson advises. “There’s no point in entering a communications war with the Russians. However, use every opportunity to prove the opposite of what they’re alleging.” Over a long career as an anti-submarine warfare officer, Jansson has come to the same conclusion. “Lie low, don’t respond to provocations. And ask yourself who benefits from the disinformation they’re spreading.”

During the 2014 hunt, Göranson tested his response concept by showing pieces of evidence, including images, at press conferences. “It’s more effective than just talking, and it creates credibility,” he said. There is, however, the risk that an initial piece of evidence turns out to be incorrect – as happened during that hunt. Nevertheless, Göranson argues that countering disinformation not with counter-propaganda but with regular factual updates is crucial.

He also suggests that journalists may need training in how to read military information, and that targeted countries should nip information about plainly false events in the bud. Several years ago, Russian-leaning Twitter accounts began circulating news about a Russian naval exercise near Swedish waters. General-assignment reporters picked up the news; naval experts commented. In short order the exercise became big news. But the Swedish armed forces didn’t react to the provocative exercise. That’s because there was no exercise—but the Swedish military’s silence created space for non-experts to define the story. “We ended up yielding the space to self-appointed experts who were clearly mistaken,” Göranson said.

The UK won’t be the last Western country to join Sweden in the targeted-by-Russian-hybrid-warfare club, which underscores a final lesson learned by Göranson: always show a united front. During the 2014 hunt, he always gave joint statements with Prime Minister Stefan Löfven and Defense Minister Peter Hultqvist. One leader can be dismissed as a clown, but there’s force in unity.