Cercando altre cose, mi sono imbattuto in questa notizia, su wikipedia:

In the border area between Russia and China, Chinese and Russian air traffic controllers observed multiple unidentified flying objects. The Russians believed they were Chinese and the Chinese believed they were Russian spy planes. On April 24, 1970, a Russian bomber disappeared during its flight from Moscow to Vladivostok without a trace. On the same day many of these objects were observed. Each attempt to shoot them down failed. By triangulation it was calculated that the UFOs came from an area in Mongolia, 1000 kilometres north of Ulan Bator. The area was bombed by a hundred Russian planes whereby a secret tunnel system was allegedly destroyed. Some rumours claim that even nuclear weapons were used. Officially these actions were referred to as a spring manoeuvre and a small border conflict.

Qualcuno ne sa qualcosa di più? Grazie.

Ciao e benvenuto. Personalmente non conosco l'argomento, ma auspico che altri (magari 'datati' come i nostri Mauro ed Enzo )possano essere d'aiuto.
Grazie e a presto,