In 1968, while the Enterprise studied Earth's past, the human agent Gary Seven sabotaged the launch of a United States orbital nuclear weapons platform.
Gary Seven was a human raised and trained by unseen aliens to keep Earth from destroying itself. Beamed toward Earth from more than a thousand light-years away, he was briefly held aboard the Enterprise, which had travelled back to 1968 for historical research, before escaping with his cat Isis to his office in New York.
There he worked with the secretary Roberta Lincoln to sabotage the launch of a nuclear warhead platform. Kirk and Spock suspected him, but history showed that the warhead exploded harmlessly high above Earth, a warning that turned people away from orbital weapons.