EDITS:
It was 1983.
Petrov identified it right away as a false alarm, since the computer system was new and poorly tested, and every hypothetical American first strike would have been larger than just four missiles.
And a side note: Petrov was actually punished for his actions because they exposed cost-cutting measures that had been taken by the party bosses in charge of the project in order to rush it out and win some substantial bonuses.
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EDITS:
It was 1983.
Petrov identified it right away as a false alarm, since the computer system was new and poorly tested, and every hypothetical American first strike would have been larger than just four missiles.
And a side note: Petrov was actually punished for his actions because they exposed cost-cutting measures that had been taken by the party bosses in charge of the project in order to rush it out and win some substantial bonuses.