This seems like a good thread to ask this question. I was reading Omni magazine back in the 1980′s, and it had an article about some sort of Roswell-like crash in the Rio Grande. That turned out to be a P-51 crashing that the locals misinterpreted, but the investigators who were debunking it came across something that surprised them: it seems that in June of 1950 or 1951, the Air force thought it saw a massive bomber formation flying over Canada(spotted by radar from Loring AFB in Maine). It was convincing enough that the British Ambassador was notified in order to evacuate Washington (no record if he did) because “we were at war”. Again supposedly “hundreds” of fighters were sent to meet this threat.
Has anybody ever heard of this? I know that there were alerts all the time, but this was taken seriously enough to alarm Washington, allegedly. And naturally, I no longer own that copy of Omni, nor remember what issue it was.