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.

At 11 p.m. one night he was ordered to scramble in his F-86D Sabre fighter to attack a “bogey” hovering above Norfolk.

Speaking about it publicly for the first time, he said: “I was told I would be firing a complete salvo, all 24 rockets. I was pumped up — this was the sort of thing that happened before a war.”

He got the UFO on his radar and closed for the attack at the Sabre’s top speed of almost 700 mph — then it disappeared off his screen in a flash.

Milton, now 77, said: “I was smoking, as fast as I could go. This thing had a different propulsion system. It was not an airplane.”

The flyer said he was visited afterwards by a sinister security official and warned not to tell anyone — so he kept silent until now.

The close encounter is in 19 files made available online yesterday by the National Archives.