A former Top Gun said Sunday he was ordered to shoot down a massive UFO over Norwich, England, 50 years ago.

RAF controllers told U.S. pilot Milton Torres to "lock on" and launch all 24 of his rockets over the city.

But as he came within seconds of firing at the alien intruder — "the size of an aircraft carrier" on his radar — it vanished at 10,000 mph.

The amazing close encounter is revealed in secret Ministry of Defense X-Files which are being declassified Monday.

Milton said, "It was some kind of alien snooping over England. I guess we'll never know what it was."

The incident happened in 1957 when Milton was a 26-year-old U.S. Air Force lieutenant based at RAF Manston in Kent, England.