Like?
Manhattan Project?
The stealth fighter, stealth bomber, the SR71, the presence of American nukes in certain countries, the existence of spy satellites, the existence of entire govt agencies, the military actions in South America related to the drug war, the many MANY covert actions accomplished against Russia during the cold war, Obamas birth place, NAVY ships that sank. The list is endless. Of course many of these have come out like most secrets do eventually.