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Leaflet describing how to recognise a foreign submarine (1980s)

How to recognise a foreign submarine

In the early 1980s, at the height of the Cold War, there were a series of incidents involving the incursion of Soviet submarines into Swedish territorial waters. In the autumn of 1980, for instance, a Swedish marine tugboat spotted the conning tower of a submarine outside Uto in the Stockholm archipelago leading to the dispatch of submarine-hunting helicopters and a prolonged submarine hunt.

A year later, in October 1981, a fisherman living in the eastern part of Kariskrona archipelago phoned the Swedish Coast Guard to say that a submarine has run aground. Despite initial doubts that any submarines could navigate in such shallow waters, the Swedish military finally visited the site and identified the sub as Soviet. The captain and crew were taken on shore for interrogation, before they and their boat were finally released.

Anxious that the Swedish military were not able to pick up these incursions, the Swedish government decided to recruit local fishermen to their submarine surveillance programme. Because of the high risk of false alarms, with fishermen frequently sighting Swedish submarines in the waters where they fished, the military came up with an idea. They issued leaflets showing the three different silhouettes of the Swedish Navy’s own submarine class and saying that if the sub you have just seen doesn’t match one of these, then “please call us”.

At about the same time that this Cold War drama was being played out, a young immunologist called Klas Karre [umlaut over a] was competing his PhD on how natural killer (NK) cells distinguish between the cells of the body (self) and foreign cells (non self). He came up with an idea he called the “missing-self hypothesis” which owned much to the submarine surveillance going on the in Baltic Sea and the leaflets issued to Swedish fishermen.

Karre later said that part of the inspiration for the missing-self hypothesis came from reading an article in the Swedish tabloid Expressen, which presented pictures of foreign submarines and of Swedish submarines. “This way, the public could learn both strategies for self/non-self discrimination: activation after recognising the unexpected [ie foreign subs] versus inactivation after recognising the expected [ie Swedish subs],” he said.

Karre, later to become professor of molecular immunology at the Karolinska Institute in Stockholm, suggested that NK cells recognise the body’s own cells by the major histocompatibility complex (MHC) class I antigens on the cell surface. If these antigens are present, the killer cells are inhibited from attacking the cells of the body. If they are absent, and the “self” is missing, then this inhibition is lifted and the foreign cells are attacked and killed by the NK cells. In effect, the MHC antigens are like the conning towers of friendly submarines. If they are present, the cell is “self”, if absent then it is “non self”.