https://en.wikipedia.org/wiki/List_of_nuclear_close_calls

This article provides a list of "nuclear close calls". If such an incident is added to the Wikipedia page that occurred between market creation and 2030, remains there for at least 2 weeks, and there are no significant doubts as to whether it occurred, this market immediately resolves YES.

Events like these often remain secret for a long time. (For example, Vasily Arkhipov's decision in 1962 to overrule Captain Savitsky and not launch a nuclear torpedo did not come to light until 2002.) Accordingly, this market won't resolve NO until I feel we can be confident none occurred; probably several decades later, when there are no longer tensions between the same countries.

In the event that Wikipedia ceases to be a reliable source, I'll consider accepting other sources. In order for such an event to qualify as a nuclear close call, it must be of comparable severity to the ones detailed in the Wikipedia article at the time I'm creating this market.

If a nuclear close call situation occurs but is not prevented, and the bomb actually detonates, that also counts to resolve this to YES. (Intentional launch does not count. It must be an accident or a decision made on bad info.)