The Norwegian Missile Crisis

Around the time of the Cold War, Norway launched a three-stage rocket that was intended for weather and scientific purposes. Unfortunately, someone forgot to tell the operators of the Russian radar systems that that was happening, so they assumed it was an Intercontinental Ballastic Missile heading toward them from the United States- declaring nuclear war. They determined that they had 8 minutes until the rocket would "impact", Russian leaders were advised and the keys that are used to launch nuclear warheads were locked in. Nuclear war was about to begin. They were told at the last minute that the rocket was from Norway for scientific purposes and they backed down.

Eventually Russia told the United States of the incident. To prevent further problems, the United States gave Russia our sophisticated radar system so that something like that would not happen again.