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OH is Finland. Oh, yeah, and the Finnish flag is on the tail.

As the first foreign connections were established, there was a demand for a country code. There was nothing official, so enthusiasts invented them themselves, and used FN, S and ES (Europe Suomi) as Finnish prefixes. S was also suggested as a prefix for the whole of Scandinavia, and the Swedes started to use SM. Finally, at the International Radio Conference in Washington, it was decided that the Finnish code should be OH, and this came into force on 1 January 1929.

http://oh2mp.ham.fi/kutsut.html

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