Over the past few days, the Swedes has been perturbed by ominous signs that appear to show a foreign submarine may have infiltrated their waters. On Friday and Saturday Swedish forces searched the waters for '‘foreign underwater activity’' in the Baltic Sea, by Sunday there were reports of three "credible" sightings. By Tuesday there were two more.

While Swedish officials haven't speculated too much about what could be out there, Swedish media has. Svenska Dagbladet has reported that radio transmissions in Russian had been detected a day before the Swedish search began. In turn, sources in the Russian Defense Ministry have denied that the submarine is theirs: It's probably Dutch, they reason.

It's all an uncomfortable hark back to Cold War embarrassment for Sweden. In the 1980s, the country suffered from a number of suspected intrusions by Soviet submarines.

Most notorious of all was the 1981 “Whisky on the rocks” incident. Here's how The Post reported that incident, under a headline "Soviet Submarine Runs Itself Aground In Restricted Waters Off Swedish Base":

"A Soviet submarine has rune aground in restricted waters near a Swedish naval base at Karlskrona on the southern Baltic Coast.

The Whisky-class submarine, which does not carry nuclear weapons, became grounded Tuesday night and was spotted yesterday by a fishing boat. it was damaged and leaking oil, but no causalities were reported.

Diplomats said the incident probably would embarrass Moscow because it would raise suspicions that Warsaw Pact vessels were spying in Swedish waters."

The Soviet Union officially apologized for the submarine's intrusion, and claimed it was accidental. A number of other apparent sightings followed, and Sweden struggled to investigate. As Peter Osnos reported for The Post in 1982, the situation had grown tense – and perhaps a little bizarre for the historically neutral Sweden:

"What baffles the Swedes is why the Soviets -- if it is in fact their submarine -- would go to such lengths to harass the country. A Defense Ministry study of the submarine problem published last month said that compared with 1980, when submarines were spotted at discreet distances from the shore, "they now act a great deal more provocatively and have been found to penetrate even deeper into our coastal waters than before."

In considering motives for such action, the study observes that if "a foreign power" intends to operate submarines in Swedish waters in wartime than "appropriate planning" will call for detailed investigation of the coastal region."

The apparent instructions were an ominous threat, and one that Sweden seemed unable to do much about. Later, The Post reported that the Swede's hunt for the submarines was becoming "an embarrassment," and that Western diplomats now believe that the repeated submarine excursions were an attempt to "harass neutral Sweden," in part due to the Soviet's own embarrassment about the "whisky on the rocks" incident.

The impact of the suspected submarines was significant. One issue was scale. A 1990 RAND Corporation report noted that the Soviet Union had "conducted submarine operations in Swedish waters continuously since World War II," but that after 1980 Swedish sources suggested a jump to between 17 and 36 foreign operations in their waters a year. That was too big to ignore for Sweden.

There was also the symbolic power. For the Swedes, it was a hurtful reminder of the relatively small scale of its military. For the rest of the world it was a sign that even in the 1980s, Russia was far from a diminished threat: Even the most well-known modern Soviet submarine tale, Tom Clancy's "The Hunt for Red October," was said to have been inspired by a mutinous Soviet submarine in Swedish waters (an incident from 1975 about which little was known).

Of course, this all died down as the Soviet Union crumbled and Russia spent much of the 1990s preoccupied with other things. If a Russian submarine has made an appearance deep in Swedish waters, it does seem like Cold War 2.0. And it's something Sweden, along with neighbor Finland, has been warning about: Earlier this year, Wilhelm Unge, the chief counter-intelligence analyst with Swedish intelligence agency Säpo, told reporters that "Russia is the biggest intelligence agent in Sweden" and warned that "you don't carry out these kinds of things unless you can actually conceive carrying out an attack in the future."

At the time, analysts said that any invasion of Sweden (or Finland) seemed unlikely. But it does beg the same question about the alleged Soviet incursions: If that really is a Russian submarine and it really is in Swedish water, what the hell is it doing there?

Whatever the reason, it's renewed debate about Swedish military spending – and, yet again, led to calls for Sweden to end its nonaligned position and finally join NATO.