Navy Regs talk about deadly force in great detail. Here are definitions and when use of deadly force is authorized:
1. DEFINITIONS
a. Deadly Force. Force that a person uses causing, or that a person knows or should know would create a substantial risk of causing, death or serious bodily harm.
b. Serious Bodily Harm. Does not include minor injuries, such as a black eye or a bloody nose, but does include fractured or dislocated bones, deep cuts, torn members of the body, serious damage to the internal organs, and other life-threatening injuries. Serious bodily harm can be applied to a person in several stages of the ladder of force. Specifically, unarmed self-defense, impact weapons and small arms fire may result in serious bodily harm.
c. Force. The amount of verbal persuasion and/or physical gestures/contact needed to gain control over a person or to direct an individual.
2. JUSTIFICATION. Deadly force is justified only under conditions of extreme necessity and as a last resort when all lesser means have failed or cannot reasonably be employed. Deadly force is justified under one or more of the following circumstances:
a. Self Defense and Defense of Others When deadly force reasonably appears to be necessary to protect law enforcement or security personnel who reasonably believe themselves or others to be in imminent danger of death or serious bodily harm.
b. Assets Involving National Security. When deadly force reasonably appears necessary to prevent the actual theft or sabotage of assets vital to national security. DoD assets shall be specifically designated as "vital to national security" only when their loss, damage, or compromise would seriously jeopardize the fulfillment of a national defense mission. Examples include nuclear weapons; nuclear command, control, and communications facilities; and designated restricted areas containing strategic operational assets, sensitive codes, or special access programs.
c. Assets Not Involving National Security but Inherently Dangerous to Others. When deadly force reasonably appears to be necessary to prevent the actual theft or sabotage of resources, such as operable weapons or ammunition, that are inherently dangerous to others; i.e., assets that, in the hands of an unauthorized individual, present a substantial potential danger of death or serious bodily harm to others. Examples include high-risk portable and lethal missiles, rockets, arms, ammunition, explosives, chemical agents, and special nuclear material.
d. Serious Offenses Against Persons. When deadly force reasonably appears necessary to prevent the commission of a serious offense involving violence and threatening death or serious bodily harm. Examples include murder, armed robbery, and aggravated assault.
e. Arrest or Apprehension. When deadly force reasonably appears to be necessary to arrest, apprehend, or prevent the escape of a person who, there is probable cause to believe they have committed an offense of the nature specified in subsections 2a through 2d above.
f. Escapes. When deadly force has been specifically authorized by the Heads of the DoD Components and reasonably appears to be necessary to prevent the escape of a prisoner, provided law enforcement or security personnel have probable cause to believe that the escaping prisoner poses a threat of serious bodily harm either to security personnel or others.