The Russians consistently violate Swedish waters with some impunity. They remain a potential threat to their nearest neighbors.
From http://en.wikipedia.org/wiki/Soviet_submarine_S-363:
In October 1981, the Russian Submarine U-137 accidentally hit an underwater rock about 2 km from the main Swedish naval base at Karlskrona. The boat was stuck on the rock for nearly 10 days. The Soviet Navy sent a rescue task force to the site in Sweden; it was composed of heavily armed destroyers and high sea tugs.When the Swedish Defence Research Agency secretly started measuring for radioactive materials through the hull, using a specially configured Coast Guard boat, they detected something that was almost certainly Uranium-238 inside the submarine. They speculated it originated from a nuclear weapon – a torpedo, in the upper port tube.[citation needed] The yield of this weapon was estimated to approximately the same as the bomb dropped over Nagasaki in 1945. However, no nuclear weapon on board U 137 was ever officially confirmed by the Soviet authorities.[1] Vasily Besedin later confirmed that there were nuclear warheads on some of the torpedoes, and that the crew was ordered to destroy the boat, including these warheads, if Swedish forces tried to take control of the vessel.[2].
Sweden's centre-right government at the time was determined to safeguard Sweden's territorial integrity. As the Soviet recovery fleet appeared off the coast on the first day, a fixed coastal artillery battery locked onto the ships, showing the Soviets that there were active coastal batteries on the islands. The fleet didn't turn immediately and as they came closer to the 12-mile (19 km) territorial limit the battery was ordered to go into war mode on its targeting radar turning it from a single frequency mode to a frequency hopping mode. The Soviet fleet reacted almost immediately to this and everything except a heavy tugboat turned and stayed in international waters, the tugboat was quickly met by Swedish torpedo boats and it left as well.
Days later as the Soviet Captain was being interrogated the weather was very bad and the Soviet submarine sent a distress call. In Swedish radar control centers the storm was interfering with the radar image. Soviet jamming could also have been a factor. As the Soviet submarine sent its distress call two ships from the nearby Soviet armada passed the 12-mile (19 km) limit headed for Karlskrona. This produced the most dangerous period of the crisis and is the time where the Swedish Prime Minister Thorbjörn Fälldin gave his famous order to "Hold the Border" to the Supreme Commander of the Swedish Armed Forces. The coastal battery now fully manned as well as the mobile coastal artillery guns and mine stations went to "action stations". The Swedish Air Force scrambled strike aircraft armed with modern anti-ship missiles and reconnaissance aircraft knowing full well that the weather didn't allow rescue helicopters to fly in the event of an engagement. After a tense 30 minutes Swedish FAC's had met the ships and identified them as West German grain carriers. The crisis was over.