Know as the White House UFO incident this is one of the most controversial sightings ever. The Air Force had ordered its jets to shoot down flying saucers and then, of course, denies it all.
On July 29, 1952, International News Service (INS) announced that the Air Force had ordered its jets to shoot down any flying saucers. The order was confirmed by an Air Force spokesperson. That same order came on the heels of a flood of flying saucer reports, particularly along the East Coast, climaxing in overflights of Washington D.C. that were picked up on radar, with jets being ordered to intercept.
On the afternoon of July 29, the Air Force called an emergency press conference to debunk the sightings and quiet the panic. It was the largest press conference since WWII.
Leading the press conference were Generals John Samford, USAF chief of intelligence, and Roger Ramey, USAF director of operations, who was in charge of jet scrambles. In July 1947, Ramey had headed the 8th Army Air Force in Fort Worth, Texas, and led the debunking of the Roswell crashed flying disk, saying it was simply a mistaken weather balloon. Samford and Ramey were called the Air Force’s top two saucer experts.
You can find all the details in this very complete Wikipedia page.