Can You Carry a Gun on a Boat in International Waters?

You can carry a gun on a boat in international waters if the vessel is U.S.-registered and you could lawfully possess the firearm at home. Beyond 12 nautical miles from any coastline, a ship answers only to the country whose flag it flies, so U.S. federal firearms law is what governs your boat. The trap is that “international waters” is a smaller slice of most trips than boaters assume. The moment you cross into another country’s territorial sea or tie up at a foreign port, that country’s laws apply, and most nations treat firearms far more strictly than the United States does.

Why U.S. Law Follows Your Boat on the High Seas

The United Nations Convention on the Law of the Sea provides that ships on the high seas are subject to the “exclusive jurisdiction” of their flag state.¹ For a U.S.-flagged vessel, that means U.S. law travels with the boat.² Federal law reinforces the point: under 18 U.S.C. § 7, the “special maritime and territorial jurisdiction of the United States” reaches U.S. vessels on the high seas, so federal criminal statutes, including federal firearms laws, apply on board.³

If you legally own a handgun or rifle under federal law and are not a prohibited person, you can have it aboard once you clear the coast. Ordinary long guns and pistols raise no federal issue in international waters.

National Firearms Act items are different. 18 U.S.C. § 922(a)(4) bars anyone other than a licensed dealer from transporting machine guns, short-barreled rifles, short-barreled shotguns, or destructive devices in foreign commerce without prior written authorization from the Attorney General.⁴ If you plan to take any NFA-regulated firearm past U.S. waters, you need ATF approval on Form 5320.20 before you leave. Without it, an otherwise lawful NFA item becomes a federal violation the moment your boat crosses into foreign commerce.⁵

Where the Legal Line Actually Sits

The ocean is not a single legal space. As you approach any coast, you pass through zones with different rules:

High seas, beyond 24 nautical miles: only your flag state’s laws govern the vessel.
Contiguous zone, 12 to 24 nautical miles: the coastal state can enforce its customs, immigration, fiscal, and sanitary laws.⁶
Territorial sea, 0 to 12 nautical miles: the coastal state has full sovereignty, and its criminal and civil laws apply to your vessel and everyone aboard.⁷

Most boaters know about the 12-mile line. Fewer know about the contiguous zone. A country that treats undeclared weapons as a customs violation can intercept and inspect starting 24 miles out, well before shore is in sight.

Innocent Passage Is Not a Firearms Exemption

International law lets ships transit a foreign country’s territorial sea under the doctrine of innocent passage, as long as the passage does not threaten the coastal state’s peace or security. That is not a pass on local firearms law. UNCLOS specifically identifies “any exercise or practice with weapons of any kind” as making passage non-innocent, and coastal states may adopt and enforce customs rules that apply during transit.⁷ An undeclared firearm aboard while you cut across another country’s territorial waters exposes you to enforcement even if you never intended to stop.

What to Do Before You Leave Port

Two pieces of paperwork matter for almost every trip, and a third matters if you own NFA items.

Register Your Firearms With CBP

Before you leave, take your firearms to a CBP office and complete Form 4457, the Certificate of Registration for Personal Effects Taken Abroad. A CBP officer verifies serial numbers and descriptions, signs the form, and returns it to you.⁸ It proves you owned the firearms before departure, which keeps CBP from treating them as foreign imports and assessing duty when you come home. The form is reusable as long as it remains legible.

You must present the signed Form 4457 to CBP on your return.⁹ Without it, expect delays and possible duty charges on your own guns.

Know the Export Limits

Taking firearms out of the country counts as an export, even on a private boat. For personal use, such as hunting or cruising, the Commerce Department’s License Exception BAG lets U.S. citizens and permanent residents temporarily export up to three firearms and no more than 1,000 rounds of ammunition per trip without a full export license.¹⁰ More firearms or more ammunition means you need separate authorization.

Suppressors, short-barreled rifles, short-barreled shotguns, and machine guns need ATF Form 5320.20 approval on top of the BAG exception.⁵

Declaring Firearms in Foreign Ports

Every country requires you to declare firearms and ammunition to customs at your first point of entry. This is not optional, and failure to declare is treated as smuggling almost everywhere. The declaration usually happens on a maritime entry form, and officials typically record serial numbers, manufacturers, calibers, and ammunition counts.

What happens next depends on the country. Three common outcomes:

Sealed storage aboard. Officials place the firearms in a locked container on the boat and apply a tamper-proof customs seal. Breaking the seal before outbound clearance is a criminal offense.
Shore confiscation for the duration of your stay. The firearms go into a government or bonded facility and come back only after you complete departure clearance.
Outright prohibition. Some countries will not allow the firearms to remain in their jurisdiction at all, even sealed aboard.

Country Rules That Catch American Boaters

The ATF publishes country-specific guidance, and a few of the most common Caribbean and Latin American destinations show how sharply rules diverge:

The Bahamas requires declaration of all firearms at the first port of entry. Only shotguns and handguns are allowed in Bahamian waters; rifles are prohibited. Declared firearms must stay on the boat and locked at all times. An undeclared firearm carries up to 10 years in prison and a $10,000 fine under the Bahamas Firearms Act.¹¹

Mexico requires a permit issued in advance by a Mexican embassy or consulate for any firearm or ammunition brought into Mexican waters. Getting caught without that permit means prison time, and Mexican authorities treat unauthorized firearms possession as a serious felony.¹¹

Jamaica, since November 2022, imposes a mandatory minimum sentence of 15 years for possession of even a single cartridge without authorization. One forgotten round in a cushion is enough.¹¹

These are three of the most popular cruising destinations for American boaters, and they are where arrests actually happen.

Self-Defense Against Piracy

Federal law does recognize why some boaters carry offshore. Under 46 U.S.C. § 8107, anyone who uses force to defend a U.S. vessel against an act of piracy is shielded from monetary liability for injuries or death to the attacker, provided the force complied with standard self-defense rules prescribed by the Secretary of the department in which the Coast Guard operates.¹² The statute defines piracy broadly to cover aggression, seizure, or restraint attempted by someone not authorized by any government or recognized international organization to enforce law at sea.

This protection reaches only the high seas, and only conduct that qualifies as piracy. It does not cover confrontations in foreign territorial waters, disputes with other boaters, or altercations that fall short of piracy. Using a firearm inside another country’s waters puts you under that country’s rules on deadly force, which are typically less forgiving than American self-defense law.

What Getting It Wrong Actually Costs

The immediate penalty for a violation is seizure of the firearm. In many countries, the vessel itself can be seized when an undeclared weapon is found aboard.¹³ Losing the boat is a real outcome, not a hypothetical.

Criminal penalties abroad are uniformly severe. Jamaica’s 15-year mandatory minimum is the extreme; the Bahamas’ 10-year maximum is more typical of the region.¹¹ The State Department cannot negotiate your release. Consular officers can visit you, provide a list of local attorneys, and notify your family, but they have no authority to intervene in another country’s legal process.

For serious violations, especially anything that looks like trafficking, a country can request an Interpol Red Notice, a worldwide alert asking law enforcement in member countries to locate and provisionally arrest a person pending extradition. A Red Notice effectively ends international travel until the matter is resolved.¹⁴

Federal penalties apply when you violate U.S. law in the process. NFA violations carry up to 10 years in prison and fines up to $250,000 for individuals. Importing firearms into the U.S. in violation of the Munitions Import List can bring up to 10 years in prison and fines up to $1,000,000.¹³

Coming Back Into the United States

Pleasure boats returning from a foreign port must report to CBP immediately on arrival. Present the signed CBP Form 4457 from before the trip. Without it, you carry the burden of proving prior ownership and face possible duty and long delays.⁹

If a foreign authority held your firearms at a bonded facility during your stay, complete that country’s outbound clearance and physically recover the weapons before you leave. Departing with a firearm still in government custody creates an open record that can complicate future visits and trigger alerts in international databases.

1
United Nations. United Nations Convention on the Law of the Sea, Part VII: High Seas
2
National Oceanic and Atmospheric Administration. Jurisdiction Over Vessels
3
Office of the Law Revision Counsel. 18 USC 7 – Special Maritime and Territorial Jurisdiction of the United States Defined
4
Office of the Law Revision Counsel. 18 USC 922 – Unlawful Acts
5
Bureau of Alcohol, Tobacco, Firearms and Explosives. Application to Transport Interstate or to Temporarily Export Certain National Firearms Act Firearms
6
National Oceanic and Atmospheric Administration. Maritime Zones and Boundaries
7
United Nations. United Nations Convention on the Law of the Sea – Part II Territorial Sea and Contiguous Zone
8
Federal Register. Certificate of Registration (CBP Forms 4455 and 4457)
9
U.S. Customs and Border Protection. Temporarily Taking a Firearm or Ammunition Outside the United States for Personal Reasons
10
eCFR. 15 CFR 740.14 – Baggage (BAG)
11
Bureau of Alcohol, Tobacco, Firearms and Explosives. Traveling with Firearms
12
Office of the Law Revision Counsel. 46 USC 8107 – Use of Force Against Piracy
13
Bureau of Alcohol, Tobacco, Firearms and Explosives. NFA Handbook – Chapter 15
14
Interpol. Red Notices