Here’s What You Need to Remember: The submarine hunt aroused domestic controversy. Swedish right-wingers saw the U-137 incident as evidence of the Soviet Union’s ill-intentions and the need to build up military deterrence. Some left-wing Swedes implied the Swedish Navy was jumping at shadows, and suggested the submarine sightings were actually NATO submarines provoking the Swedes against the Soviets.

On the morning of October 28, 1981, two Swedish fishermen were hauling their catch back to Karlskrona when they noticed a mysterious oil slick. One Bertil Sturkmen later returned to the area to investigate, and at 10 a.m. came across a startling sight: a seventy-six-meter long submarine wedged on its starboard side against the sharp rocks of Torumskär island. An officer was standing on the submarine’s conning tower, staring at him through binoculars—and holding a machine gun.

Sturkmen sailed back to Karlskrona and notified the nearby Swedish naval base, which harbored two of Sweden’s three coastal defense flotillas. Karlskrona was well protected from attack due to its position in a shallow bay shielded by a belt of rocky islands which demanded careful circumnavigation. Somehow, the submarine had wended it way through this daunting aquatic obstacle course to a point only six miles away from the base.

The patrol boat Smyge reached the grounded vessel by 11 a.m., and Comm. Karl Andersson managed to converse with a crew members in German—who informed him that the submarine had strayed off course due to a faulty navigation system.

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The boat in question was S-363, a Soviet Whiskey-class coastal patrol submarine—thus giving the incident its moniker “the Whiskey on the Rocks.” (At the time, the submarine was widely mis-identified as U-137.) The short-range diesel-electric submarine had a crew of 56 and had been designed in the 1940s with snorkel and battery technology derived from the Nazi Type XXI “electric boat.” The Soviet Union built more than two hundred of the submarines.

Sweden’s long Baltic coastline faced Leningrad and Soviet bases in the Baltic states and Poland. Though international law states that a country’s territorial waters extend twelve nautical miles (fourteen miles) away from its mainland and island possessions, Soviet submarines had been detected intruding into Swedish waters on numerous occasions during the 1960s and 1970s. Swedish vessels had opened fire on them several times without apparent effect.

Sweden was theoretically neutral during the Cold War, but Stockholm’s perceived closeness to the West apparently motivated Soviet intelligence-gathering activities. The Swedes returned the favor by shadowing Soviet ships and aircraft with their own jets and submarines, occasionally leading to tense situations: for example, in 1985 a standoff between Swedish Viggen and Soviet Su-15 interceptors resulted in a deadly crash.

In fact, the evening before, on October 27, the Swedish submarine Neptune and two helicopters had been testing a new type of torpedo which may have been of considerable interest to the Soviets. It was around that time that S-363 ran aground. Her crew gunned her diesel engines trying to escape—producing a din which was heard ashore.

As news of S-363’s grounding spread, journalists and boats surrounded the submarine. Stockholm demanded the right to interrogate her captain, Anatolij Gustjtjin. Moscow claimed S-363 had entered Swedish waters seeking aid, though of course S-363 had not issued a distress signal.

Swedish radars then detected a task force of a dozen Soviet ships approaching S-363. Led by Admiral A. Kalinin, the fleet included the missile destroyer Obraztsovy, and older gun-armed destroyer, two anti-ship missile boats, a frigate and a tug.

While the submarine Neptune did its best to slow down the approaching fleet, the icebreaker Thule was moved into position to block access to S-363. As the Soviet task force continued to approach, radar-guided coastal guns activated their targeting radars, which were designed to hop multiple frequencies to evade counter-battery fire. This finally prompted the Soviet warships to halt. A lone tug continued approaching, however, until Swedish torpedo boats barred it progress.

Meanwhile, Swedish ships conducted gamma-ray spectroscopic analyses of S-363 and detected trace amounts of what appeared to be Uranium 238—suggesting that a nuclear weapon was on. Back in the 1950s, the Soviet Union had develop several nuclear torpedoes, including smaller types designed to knock out multiple enemy vessels, as well as a larger type for nuking naval bases and coastal cities—a concept which has recently seen a renaissance. Indeed, the Whiskey-class S-144 had tested a T-5 anti-ship nuclear torpedo with a five-kiloton warhead in 1957.

After days of protracted negotiations, Captain Gustjtjin, accompanied by political officer Vassily Besedin, submitted himself to a six-hour interrogation aboard the torpedo boat Vastervik on November 2. He insisted that S-363 had experienced a breakdown of its four different navigational systems and drifted a hundred miles off course from the coast of Poland. However, given that entering that far into Karlskrona Bay required numerous precise maneuvers, his Swedish interlocutor noted such a mistake was “worthy of the Guinness Book of World Records.”

Meanwhile a storm broke out, obscuring Swedish radars. When it cleared, two vessels were detected approaching Swedish waters. Assuming a renewed Soviet incursion, Prime Minister Falldin had naval strike planes scrambled and coastal guns put on standby to open fire in defense of territorial waters. But after twenty minutes, it was discovered that the contacts were German merchant ships.

Finally, after a ten-day standoff, Moscow permitted the Swedes to extricate the grounded submarine. Swedish tugs put the Soviet sub back to water and handed her off to Admiral Kalinin’s task force. S-363 returned to port November 7.

Political officer Besedin later told a Swedish journalist:

"Our officers were ordered to blow up the submarine together with its crew if the Swedish military forces tried to take possession of the boat. These orders would have been completed.

"Onboard, in the torpedo tubes, there were torpedoes with nuclear warheads. The effect of detonating such nuclear warhead is about the same as the impact of the bomb released over Hiroshima [15 kilotons]. It is terrible to think of all the destruction and the long-term consequences it would have had for Sweden as a whole."

Karl Andersson has questioned Besedin’s account, however, arguing that the submarine would have been scuttled by destroying the propeller shaft and valves, not detonating onboard nuclear warheads.

Besedin also insisted that a navigational error had occurred due to damage from an earlier collision, forcing S-363’s crew to rely on less accurate methods. Another theory is that the submarine was testing a new, unreliable inertial navigation system.

The episode precipitated a decade of intensified submarine hunts by the Swedish Navy. However, despite deploying numerous torpedoes, depth charges and mines at numerous dozens of contacts, no Soviet submarines were apparently destroyed. Stockholm also began working on upgrading the stealth and endurance of its coastal defense submarines by developing advanced Air-Independent Propulsion technology.

The submarine hunt aroused domestic controversy. Swedish right-wingers saw the U-137 incident as evidence of the Soviet Union’s ill-intentions and the need to build up military deterrence. Some left-wing Swedes implied the Swedish Navy was jumping at shadows, and suggested the submarine sightings were actually NATO submarines provoking the Swedes against the Soviets.

The submarine infiltrations appeared to cease with the end of the Cold War—but not for good. As relations between Russia and the West sharply deteriorated in 2014 over Moscow’s seizure of the Crimean Peninsula from Ukraine, the Swedish Navy spent a week attempting to track a mini-submarine which reportedly sighted multiple times in Swedish waters.

Sébastien Roblin holds a Master’s Degree in Conflict Resolution from Georgetown University and served as a university instructor for the Peace Corps in China. He has also worked in education, editing, and refugee resettlement in France and the United States. He currently writes on security and military history for War Is Boring. This article first appeared several years ago.

Image: Reuters.