After Israel attacked its Arab enemies during the 6 day war in June 1967, it then proceeded to attack its ally: The United States, in the form of the U.S.S. Liberty, a surveillance vessel, which was monitoring the ongoing war.
The United States assumed that Egypt had conducted the attack on the U.S.S. Liberty, and launched an aircraft loaded with an atomic bomb, with instruction to drop the atomic bomb on Cairo, Egypt.
Later, the U.S. was made aware that the attack on the Liberty was conducted by Israel. It then recalled the aircraft back to its carrier.
Courtesy of the: BBC