During the Cold War, every country was paranoid - and that includes Sweden - to the point where a diplomatic crisis was almost started by fish farts.
In 1981, a Soviet submarine ran aground off the coast of Sweden, only 10 kilometers away from a Swedish military naval base. The crew said that due to problems in their navigational instruments, they were forced to enter Swedish waters.
It turns out that, although we usually don't take this into account, Sweden's military industry is very good. During the Cold War, Sweden remained a neutral country. However, they are located in close proximity to Russia, creating a great deal of mistrust. During this period, Sweden invested a considerable amount of money and manpower in its military.
In World War I, the country remained neutral and profited from arms exports, developing its arms sector. In World War II, it again developed war technology, but this time to protect itself from invasions by both the Allies and the Germans, and to remain neutral, as historically. During the Cold War, while remaining neutral, it developed its war technology, both toprotection, as well as for export.
Gripen NG, a flagship product of the Swedish war industry (G4ng3r / Wikimedia Commons).
Russia is historically a very imperialist country, so during the Cold War Sweden was on alert because of its proximity to the Soviet Union. When that submarine entered Swedish waters, the Swedish military detected radioactive war materials, which indicated that it was equipped with nuclear weapons.
They returned the submarine, rather than seizing it. However, they kept an even closer eye on Soviet movements near southern Sweden. During this period, they detected a series of strange signals below the water in 1982.
Convinced that they were Russian submarines, they immediately deployed their armed forces to pursue them. For a month, Swedish submarines, boats and aircraft pursued the signals, but failed to find any enemy intruders. For another 15 years, they continued to pursue the sound signals and vibrations picked up underwater, but never found anything.
They believed that, with the end of the Cold War, the already weakened Russians would stop provoking them, as there were too many internal issues for the countries of the former Soviet Union to solve. However, during the early 1990s, already with the fall of the USSR, the signals were unbroken - and the Swedes remained perplexed.
Diplomatic crisis over ... fish farts?
Herring, the 'Russian submarine' (Gervais and Boulart, 1877).
In 1996, Magnus Wahlberg, a professor at the University of Southern Denmark, joined the mobilization investigating the alleged Russian submarines. Then the military took him and other civilians involved to a secret room in a naval base to show them the sounds captured from inside the water. Until then, only military personnel knew about it.
So Wahlberg and another colleague started trying to figure out what caused those sounds, working with the hypothesis that they might not actually be Russian nuclear submarines. What would make so many bubbles and sounds to the point of confusing the entire military of a country so competent in that business?
"It turns out that the herring has a swim bladder, and that swim bladder connects to the fish's anal duct. It's a unique connection, found only in herring. So a herring can squeeze out its swim bladder, and in that way it can release a small number of bubbles through the anal opening," explains the professor in a lecture at the TED Talks in 2012.
Herring walk in large shoals. When in a stressful situation, such as water too agitated (by military activities pursuing them) or predators threatening them, they release gases similar to flatulence, i.e. farts. Do you know that song: "one elephant doesn't bother many people; two elephants bother a lot more"? Well, this is also true for herring. Giant shoals madeall that noise.
See Magnus Wahlberg's talk at TED Talks in 2012:
With information from IFL Science