It was discovered the next day - on October 28th - by a local fisherman, says Andreas Linderoth, a historian and a research coordinator at the Naval museum in Karlskrona.
"The submarine that had ran aground flew a flag that he didn't recognize, and he knew instantly that it wasn't a Swedish submarine, but the fisherman didn't want to make a big fuzz about it and went on his business. Later on he told a neighbour about it, and the neighbour then called he naval base to let them know that there probably was a Russian submarine in the archipelago. The people at the naval base could hardly believe their ears when they got this message," Linderoth says.
Not only had the submarine entered Swedish waters without permission, but what made the incident even more controversial was that the sub had ran aground in a restricted military zone no more than a few kilometers from an important Swedish naval base.
The news about the stranded foreign sub quickly reached the Swedish government that decided to let the sub remain on the rocks until the Armed Forces had established which country it was from and why it had ended up so deep into Swedish territory.
Naval officers from the army were sent out to speak with the submarine's commanding officer and once they had confirmed that it was a Soviet submarine, the Swedish government demanded that the Soviet union let the Swedish Armed Forces examine the logbooks onboard and interrogate the commanding officer.
"At the same time, the Soviets had a rescue fleet on its way towards Sweden. The message from the Swedish government was to stop any foreign ships from entering Swedish waters, so at that time the situation was quite tense," Linderoth says.
Back at the submarine, the commanding officer had told the Armed Forces that they were on a training mission in the Baltic and that they had no idea where they were because all of their navigation aids had failed at the same time.
"He didn't give any informative or more conclusive answers to what the Soviet union had in mind when they, perhaps, sent a submarine into Swedish waters. It's still unknown today if it was simply a mistake by the commanding officer or if he was on some sort of secret mission in Swedish waters," Linderoth says.
The Soviet rescue fleet never entered Swedish waters, and after a few days a Swedish tugboat escorted the submarine back into international waters after the Soviet Union had agreed to cover all the expenses, but the incident of the stranded submarine shaped Sweden for years to come, according Andreas Linderoth.
"I would say that this was kind of an eye-opener, that Sweden was not the kind of country that could be isolated in between the two superpowers in the cold war. It was not possible to find a third way between capitalism and communism. I think the submarine incidents have made people understand that Sweden is affected by events happening around us," Linderoth says.
Throughout the rest of the 1980's, the Swedish Navy swept the Baltic Sea for more Soviet submarines and launched several high-profile submarine hunts within Swedish waters, but they could never say with certainty that another sub had breached Swedish territory. Then last year, after two quiet decades, the submarine threat surfaced again when a civilian spotted what he was sure of was a submarine outside of Stockholm.
"It was almost like you were thrown back to the 1980's. The headlines in the newspapers and the reports on the news were almost the same as in the 1980's. So, you could say that history almost repeats itself some 30 years later when there were new submarine incidents in Sweden, Linderoth says.