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 to trigger such retaliation.
[1] An example of the implementation of such a strategy could be: US Navy ballistic missile submarines are ordered to surface at periodic intervals to receive communications indicating that no change has occurred in the defense condition.
Should the submarines be unable to receive the proper command and control signals indicating normal, peacetime conditions, their orders would be to launch their nuclear missiles under the assumption that command and control structures had been destroyed in a nuclear attack and that retaliation was therefore necessary.
This approach is obviously exceptionally dangerous for a variety of reasons, as any benign communications disruption due to technical failure could conceivably incite an unnecessary nuclear war.
The strategy's intended value lies in deterrence against attack on command, control, communications, and computer (see C4I) networks by any potential adversary.