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On 6 September 1976, an aircraft appears out of the clouds near the Japanese city of Hakodate, on the northern island of Hokkaido. It’s a twin-engined jet, but not the kind of short-haul airliner Hakodate is used to seeing. This huge, grey hulk sports the red stars of the Soviet Union. No-one in the West has ever seen one before.

The jet lands on Hakodate’s concrete-and-asphalt runway. The runway, it turns out, is not long enough. The jet ploughs through hundreds of feet of earth before it finally comes to rest at the far end of the airport.

The pilot climbs out of the plane’s cockpit and fires two warning shots from his pistol – motorists on the road next to the airport have been taking pictures of this strange sight. It is some minutes before airport officials, driving from the terminal, reach him. It is then that the 29-year-old pilot, Flight Lieutenant Viktor Ivanovich Belenko of the Soviet Air Defence Forces, announces that he wishes to defect.

It is no normal defection. Belenko has not wandered into an embassy, or jumped ship while visiting a foreign port. The plane that he has flown 400-odd miles, and which now sits stranded at the end of a provincial Japanese runway, is the Mikoyan-Gurevich MiG-25. It is the most secretive aircraft the Soviet Union has ever built.

Until Belenko’s landing, that is.

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The West first became aware of what would become known as the MiG-25 around 1970. Spy satellites stalking Soviet airfields picked up a new kind of aircraft being tested in secret. They looked like enormous fighter planes, and the West’s militaries were concerned by one particular feature; they sported very large wings.