fail-deadly

{{Short description|Concept in nuclear military strategy}}

Fail-deadly is a concept in nuclear military strategy that encourages deterrence by guaranteeing an immediate, automatic, and overwhelming response to an attack, even if there is no one left to trigger such retaliation.{{Citation needed|date=April 2025}} The term fail-deadly was coined as a contrast to fail-safe.

Fail-deadly can refer to specific technology components, or the controls system as a whole. The United Kingdom's fail-deadly policies delegate strike authority to submarine commanders in the event of a loss of command (using letters of last resort), ensuring that even when uncoordinated, nuclear retaliation can be carried out.{{cite book |last=Scott |first=Len |date=2000 |title=Planning Armageddon |url=https://books.google.com/books?id=lWNwZZ1tV_8C&pg=PA301 |location=Amsterdam |publisher=Overseas Publishers Association |isbn=9058230066 |page=301 }}