Definition of "fail-deadly"
fail-deadly
adjective
not comparable
(military) Of a nuclear weapons strategy: encouraging deterrence by guaranteeing an automatic, immediate, and overwhelming response to an attack, even if the command-and-control infrastructure has been damaged by the enemy's first strike.
Quotations
One, admittedly extreme, means of reducing the impact of a command, control, and communication failure would be the adoption of a "fail deadly" mode of operation. For example, as opposed to requiring a positive signal to proceed on to target after launch-on-warning, airplanes might be permitted to continue until a negative recall signal were received. The risk of unauthorized action would be increased, as would the danger of accidental or inadvertent war due to equipment malfunction.
1976 May 15, Lewis A. Dunn, Herman Kahn, “Parameters of Nth Country Nuclear-weapon Programs and Postures”, in Trends in Nuclear Proliferation, 1975–1995: Projections, Problems, and Policy Options: Final Report (HI-2336/3-RR), Croton-on-Hudson, N.Y.; Paris: Hudson Institute, page 92
If one were to assume a more traditional Realist image of human fallibility, then one's confidence in the safety of the elaborate nuclear "fail deadly" deterrence order might not be so sanguine.
1993, Daniel Deudney, “Dividing Realism: Structural Realism versus Security Materialism on Nuclear Security and Proliferation”, in Zachary S. Davis, Benjamin Frankel, editors, The Proliferation Puzzle: Why Nuclear Weapons Spread (and What Results) (“Security Studies” Special Issue), Abingdon, Oxfordshire; New York, N.Y.: Routledge, published 2021, part I (Realist Approaches), page 17
[F]ail-deadly is a concept from nuclear military strategy, suggesting deterrence by an immediate and forceful response to an attack. It is interesting to investigate what differentiates these two design approaches to security protocols, and what they have in common when we consider a family of protocols where both fail-safe and fail-deadly versions are considered.
2018, “Preface”, in Vashek Matyáš, Petr Švenda, Frank Stajano, Bruce Christianson, Jonathan Anderson, editors, Security Protocols XXVI: 26th International Workshop, Cambridge, UK, March 19–21, 2018: Revised Selected Papers (Lecture Notes in Computer Science; 11286), Cham, Zug, Switzerland: Springer Nature Switzerland, page v