What Is the Navy’s Definition of Deadly Force?

The Navy’s definition of deadly force follows the Department of Defense standard: force that is likely to cause, or that a person knows or should know would create a substantial risk of causing, death or serious bodily harm.¹ The definition turns on the probable outcome, not the tool. A rifle shot obviously qualifies. So does striking someone with a vehicle, or shoving a person from a height, if the likely result is death or grave injury. Under Navy and DoD policy, that level of force is authorized only in a short list of situations, only as a last resort, and only in an amount proportional to the threat.

What Counts as Serious Bodily Harm

The definition rides on the phrase “serious bodily harm,” and DoD draws that line deliberately. A black eye or a bloody nose does not qualify. Broken or dislocated bones, deep lacerations, torn limbs, damage to internal organs, and any other injury that threatens life do qualify. The entire legal justification for a lethal response depends on whether the threat you face reaches that threshold, so the distinction matters before you ever put a hand on a weapon.

When Deadly Force Is Authorized

DoD policy lists a narrow set of circumstances that can justify deadly force. Each one still requires a reasonable belief that the threat is imminent.²

Self-Defense and Defense of Others

Every service member keeps the inherent right to self-defense. Deadly force is justified when you reasonably believe you face an imminent threat of death or serious bodily harm. The same authority extends to protecting other people, whether fellow service members or civilians, when the threat is immediate and connected to your assigned duty.

Assets Vital to National Security

Some assets carry a “vital to national security” designation, meaning their loss or compromise would seriously jeopardize a national defense mission. Nuclear weapons and nuclear command-and-control facilities are the standard examples. Deadly force may be used to prevent their theft or sabotage. The designation is deliberately narrow; expensive or sensitive equipment does not automatically qualify.

Inherently Dangerous Property

Certain items are dangerous enough that letting them fall into the wrong hands would itself create an imminent threat of death. Portable missiles, rockets, arms, ammunition, explosives, chemical agents, and special nuclear material fall into this category. The justification here is about what the object can do in unauthorized hands, not what it costs.

Serious Offenses Against Persons

Deadly force may be used to stop a serious violent crime in progress, such as kidnapping, sexual assault, or any offense that carries an imminent danger of death or serious bodily harm to the victim. The emphasis is on imminence. The offense has to be happening or about to happen, not something merely feared for later.

Apprehension and Preventing Escape

Deadly force may be used to arrest or apprehend someone reasonably believed to have just committed one of the serious offenses above. It may also be used to prevent the escape of a prisoner who poses an imminent threat of death or serious bodily harm to others, though escape-related deadly force generally requires specific authorization from the Secretary of the Navy. A fleeing shoplifter does not meet this standard. The person must present a genuine risk of serious violence.

Necessity and Proportionality

Falling within one of those situations is necessary but not sufficient. Two further tests run through every deadly-force decision.

Necessity. Deadly force is a last resort. All lesser means must have failed, be unavailable, or be unable to reasonably address the threat before lethal force enters the picture. That standard does not require exhausting every conceivable option in a split-second crisis, but it does mean that if verbal commands or physical control could realistically resolve the situation, going straight to a firearm is not authorized. When feasible and safe, a verbal warning (typically an order to halt) must be given before firing.

Proportionality. The force used must be reasonable in intensity, duration, and scope relative to the threat. Once the threat is neutralized, force must stop. Continuing to fire after a person is down and no longer a threat is not proportional and is not lawful. Every shot must also account for the safety of bystanders who are not part of the threat.

Navy training reflects this through a use-of-force continuum that runs from verbal commands, through empty-hand control, to less-lethal tools such as pepper spray and batons, and only then to deadly force. The continuum works in both directions. As a threat de-escalates, the force level must come down with it. SECNAVINST 5500.37 requires that armed Navy and Marine Corps personnel have access to less-lethal options and consider them before resorting to firearms.³

Where the Rules Come From

Three layers of authority govern deadly force in the Navy, each narrowing the one above it.

The Uniform Code of Military Justice, codified in Chapter 47 of Title 10, is the criminal code that applies to every service member and establishes the articles under which unauthorized or excessive force is prosecuted.⁴
DoD Directive 5210.56 sets the department-wide policy on arming personnel and authorizing force. It defines deadly force, lists the situations that justify it, and requires that lethal force be a last resort.¹
SECNAVINST 5500.37 implements DoDD 5210.56 for Navy and Marine Corps personnel. It replaced the earlier SECNAVINST 5500.29 series and covers everything from who can authorize arming to when arming authority must be suspended after an incident.³

On top of these standing rules, operational commanders issue Rules of Engagement for specific missions. The Chairman of the Joint Chiefs publishes Standing Rules of Engagement and Standing Rules for the Use of Force through CJCSI 3121.01B, which govern self-defense and force decisions across military operations. Theater or mission-specific ROE can tighten those standards further but cannot loosen them below the DoD baseline.

What Happens if Deadly Force Is Used Outside These Limits

Using deadly force outside the authorized framework triggers both criminal prosecution under the UCMJ and administrative fallout. The charge depends on the circumstances and the outcome.

Murder under Article 118 covers an unlawful killing committed with premeditated intent, intent to kill or inflict great bodily harm, or through an inherently dangerous act showing wanton disregard for human life. Premeditated murder and felony murder carry a mandatory sentence of death or life imprisonment.⁵
Manslaughter under Article 119 covers unlawful killings committed in the heat of sudden passion caused by adequate provocation (voluntary) or resulting from culpable negligence (involuntary).⁶
Aggravated assault under Article 128 applies when excessive force causes serious harm short of death, including assault with a dangerous weapon or infliction of substantial or grievous bodily harm.⁷
Violating Rules of Engagement, which are lawful orders, can be charged separately under Article 90. In wartime, willful disobedience of a superior commissioned officer’s lawful command carries a potential death sentence.⁸

Administrative consequences can arrive before any court-martial. SECNAVINST 5500.37 requires arming authorities to retrieve government-issued firearms and ammunition from anyone no longer qualified to be armed, including a service member facing charges that could lead to disqualification.³ Arming authorization can be suspended, weapons retrieved, and the member removed from security duties while the incident is reviewed. The criminal and administrative tracks run independently, and a favorable outcome on one does not decide the other.

1
Department of Defense. DoDD 5210.56 – Arming and the Use of Force
2
Federal Register. Carrying of Firearms and Use of Force for Law Enforcement, Security, Counterintelligence, and Protective Services
3
Department of the Navy. SECNAVINST 5500.37 CH-1 – Arming and the Use of Force
4
Office of the Law Revision Counsel. 10 USC Ch. 47 – Uniform Code of Military Justice
5
Office of the Law Revision Counsel. 10 USC 918 – Art. 118. Murder
6
Office of the Law Revision Counsel. 10 USC 919 – Art. 119. Manslaughter
7
Office of the Law Revision Counsel. 10 USC 928 – Art. 128. Assault
8
Office of the Law Revision Counsel. 10 USC 890 – Art. 90. Willfully Disobeying Superior Commissioned Officer