Bruce Brill, a former translator for the National Security Agency, discovered the U.S. intelligence agencies had secret divisions called "Jew Rooms" working against Israel and knew in advance that the Arab nations would attack Israel on Yom Kippur 1973.
Brill later discovered not only did the intel community know about the impending attack, but a secret division inside the CIA misled Israel, assuring their Israeli counterparts there would be no attack.