Yoooo, there were two incidents in which a Soviet service member saved the world by refusing to fire nukes. One was during the Cuban missile crisis. The USA blockaded Cuba in response to the USSR placing nuclear missiles there. A Soviet nuclear-armed submarine went down under a US naval ship. The ship started throwing dummy charges over to scare the submarine to come out. The sub hadn't had any comm with the USSR in days and thought they were under attack. Two of the three officers needed to approve a nuclear torpedo strike argued for the strike. The other, Vasily Arkhipov, declined despite the other officers insisting. Arkhipov was able to convince the other two to not strike and bring the sub up to reconnect comm with Moscow. The immediate conflict eventually ended with no casualties or strikes. Had they fired a nuclear torpedo, it could have led to a nuclear war.
The other was pretty close too. Three weeks before the incident, a Korean airliner full of civilian passengers accidentally flew into prohibited Soviet airspace due to a navigation error. The Soviets thought it was a US spy plane and shot it down, killing everyone on board. Tensions were high af. Three weeks later, Soviet surveillance equipment showed that the USSR was being attacked with 5 nuclear missiles by the US. Stanislav Petrov saw the incoming missiles and decided to not report the info further up the command because he thought there was no way an American first strike would only be five missiles. He waited for confirmation of the missile strike from the ground, which never came. After a while, it was evident that the system had a malfunction. They eventually discovered that a rare coincidence between the Sun, some clouds, and the Soviet satellites resulted in the false alarm. Had Petrov reported the incoming strike, it is quite possible that higher command would have ordered a "counter" nuclear-strike because of their view of the US.
Both of these incidents were scary close to ending the world as we know it. It wouldn't have just destroyed the USA and USSR. Aside from the direct attacks and destruction of infrastructure and institutions in the stated countries, the strikes would have resulted in a nuclear winter and eventual worldwide famine for over a decade.
