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Sweden’s famed neutrality has often proved to be a somewhat flexible concept: occupying a central position in northern Europe, but with a smaller population than many of their neighbors, the Swedes have often had to make compromises to maintain their independence. During World War I, Sweden helped German intelligence eavesdrop on telegraph communications between Russia and the U.K., and during World War II, it supplied iron ore to Nazi Germany and allowed German troops to move across its territory.

With Swedish neutrality looking more theoretical than real, the only question U.S. spooks had during the Cold War was how to get Sweden on their side. This was tricky: a proud, democratic people, the Swedes were likely to react negatively to overt attempts to manipulate them, for example through bullying or bribery. But what if you make it look like it’s the other guy who’s doing the bullying?

While risky, this kind of “false flag” operation is considerably easier to pull off when no one can see exactly what the heck is going on… because it’s mostly happening underwater.

Of course, you still need a plausible premise for the international head games. Fortunately the Soviets helped out by just doing what they do (or, uh, did).

Whisky on the Rocks

On October 27, 1981, the S-363 -- a 250-foot, Soviet Whisky-class diesel attack submarine -- ran aground on an island in the Baltic Sea near the southern Swedish town of Karlskrona, which is also the site of a large Swedish naval base. The submarine was deep inside Swedish territorial waters -- needless to say, without permission -- in a blatant violation of Swedish sovereignty; even worse, it was armed with at least one nuclear weapon.

A predictable uproar ensued, with Swedish politicians uniting to condemn the Soviet Union’s illegal actions, while the Soviets offered lame excuses for the mishap, which the Western press dubbed “Whisky on the Rocks.” But it was perfectly clear that the sub had been snooping on Swedish naval defenses. A former Soviet intelligence officer later revealed that the submarine probably ran aground because its crew was intoxicated (drunk spying = you’re doing it wrong). A Soviet rescue fleet was forced to withdraw after the Swedes threatened it with coastal artillery, planes, and torpedo boats. The Swedes eventually gave the stricken S-363 back to the Soviets, but the whole thing was basically a hopeless diplomatic debacle for the Soviet Union.

With the scene set, American and British intelligence quickly moved to exploit the opening provided by Soviet bungling with a series of “false flag” missions, in the form of submarine intrusions, which the Swedes also blamed on the Soviet Union. According to Ola Tunander’s book The Secret War Against Sweden, the intrusions were designed to create the appearance of escalating Soviet infringement of Swedish neutrality -- when in fact it was American and British submarines all along. And it worked like a charm.

Naval Whack-A-Mole

In October 1982, the sighting of an unknown periscope set alarm bells ringing in the Swedish military, leading to a series of submarine “hunts” by the Swedish navy, some targeting the elusive vessels with depth charges and mines. These came to resemble a frantic game of “whack-a-mole,” as submarine periscopes popped up and then disappeared with infuriating frequency along the Swedish coast; the Kremlin, it seemed, wanted to really rub the intrusions in Sweden’s face.

The hunts themselves were far from secret: one naval exercise in the Harsfjarden archipelago, lasting several weeks, was covered by 750 journalists from all over the world. Following the S-363 scandal, the Swedish government intended these high-profile events to show both Swedish voters and the Soviets that no one was going to kick Sweden around.

Despite the liberal use of explosives -- which actually damaged several of the mystery vessels on at least one occasion -- the Swedish navy never managed to destroy one, so it never gathered any hard evidence (hull debris, uniforms, etc.) that the Soviets were actually to blame. Indeed, one of the submarine contacts was explicitly described in the Swedish navy’s official war diary as “not Warsaw Pact.” Nonetheless, a report to Sweden’s parliament later concluded that a total of six Soviet submersible vessels had “played their games” in Swedish territorial waters during the intrusions. The alleged intruders included three full-sized submarines, two midget subs, and a submarine crawler that supposedly crept along the ocean floor, penetrating Stockholm harbor to within a few hundred feet Sweden’s royal palace. Of course, the Soviets denied up and down that they had violated Swedish neutrality… because they hadn’t; but of course, the Swedes didn’t believe the Soviets… because who would?

Score one major diplomatic victory for the U.S.: the proportion of Swedes who viewed the Soviet Union as a direct threat increased from 6% in 1976 to 45% at the end of 1983, while those who viewed the Soviet Union as unfriendly increased from 27% to over 80%. Over the same period, the proportion of Swedes who favored increased defense spending increased from around 15% to over 50%. Perhaps most importantly, the U.S. also undermined the left-wing government of prime minister Olof Palme. Following the sub hunts, Palme -- who had angered the U.S. by sympathizing with Third World communist regimes -- faced allegations that there was a Soviet spy in his cabinet, as well as unprecedented criticism from his own military commanders (he was later assassinated in mysterious circumstances).

But despite the hullabaloo, there was never any evidence the Soviets were responsible. Incredibly, the only Swedish tapes of the submarine propeller sounds from the Harsfjarden hunt, which might have helped identify the vessels, were curiously erased. Meanwhile, U.S. intelligence confiscated the only other recording from the Harsfjarden hunt, held by Norway, a U.S. ally in NATO. A third recording, supposedly from a later intrusion, turned out to be a mink (an otter relative). Photos of periscopes and surfaced submarines taken by Swedish naval observers and journalists also disappeared from Swedish newspaper archives.

So if there wasn’t any evidence the Soviets were responsible, how can we be sure American and British subs were the actual culprits? Well, we can’t -- that’s kind of the whole point -- but there’s good reason to be suspicious. While we don’t have specific information about Western submarine maneuvers during the period of the intrusions, former U.S. Secretary of Defense Caspar Weinberger admitted in an interview in 2000 that U.S. submarines “regularly” entered Swedish territorial waters to “test” Swedish defenses in the early 1980s. Several British submarine commanders also admitted to carrying out secret operations in Swedish waters during this time. And it seems odd that the Soviets -- who freaked out about the S-363 -- never made a peep when the Swedish navy damaged several more of “their” submarines during the sub hunts.

Erik Sass is the author of The Mental Floss History of the United States and co-author with Steve Wiegand of The Mental Floss History of the World, both of which you should go buy right now. When he’s not writing about historical curiosities for mental_floss, he covers online and traditional media for MediaPost. His interests include water gardens, games of strategy, geography, and cats.