Barrett et al. (2013) distinguish between accidental/unauthorised, inadvertent, and deliberate nuclear launches or detonations:

• "In an accidental or unauthorized launch or detonation, system safeguards or procedures to maintain control over nuclear weapons fail in such a way that a nuclear weapon or missile launches or explodes without direction from leaders."

• "In an inadvertent detonation, the attacking nation mistakenly concludes that it is under nuclear attack and launches one or more nuclear weapons in what it believes is a counterattack."

• In a deliberate detonation, the attacking nation decides to launch one or more nuclear weapons either in response to a genuine nuclear attack or without believing that it is under nuclear attack.

The only non-test nuclear weapons to date, by the US in 1945, were both deliberate. But a future nuclear conflict could in theory begin with any of those three types of detonations, which could then be followed by detonations from the same or other types.