Chapter 5: Sovereign Immunity

Sovereign Immunity


It is a long-standing rule of international law that one sovereign State does not have authority over another sovereign State and that all States are equals. This underlies the concept of sovereign immunity. Sovereign immunity in international law makes one State’s property immune from interference by another State in two ways: jurisdictional immunity, which limits the adjudicatory power of national courts against a foreign State, and enforcement immunity, which limits the taking of or interference with State property by executive authorities of foreign States.

The LOSC Articles on Sovereign Immunity

Sovereign immunity for vessels owned or operated by a State and used in governmental, non-commercial service has been recognized in U.S. law, customary international law, and international agreements. In The Schooner Exchange v. McFaddon,1 the U.S. Supreme Court recognized in 1812 that U.S. courts have no jurisdiction over military vessels in the service of another sovereign State, as warships are regarded as political and military instruments of the State. Customary norms of international law concerning State-owned vessel and warship immunity are reflected in the United Nations Convention on the Jurisdictional Immunities of States and Their Property, the International Convention for the Unification of Certain Rules Relating to the Immunity of State-Owned Vessels, and the LOSC.

Article 29 of the LOSC defines a warship as, “[A] ship belonging to the armed forces of a State bearing the external marks distinguishing such ships of its nationality, under the command of an officer duly commissioned by the government of the State and whose name appears in the appropriate service list or its equivalent, and manned by a crew who are under regular naval discipline.”2 Under this definition, a ship does not need to be armed in order to be considered a warship. Articles 95 and 96 of the LOSC recognize the complete immunity of warships and other government ships operated for non-commercial purposes on the high seas. 3 Regarding the territorial waters of a coastal State, Article 32 reaffirms “the immunities of warships and other government ships operated for non-commercial purposes”, but a coastal State may require a warship to leave its territorial sea if the warship does not comply with the laws and regulations of the coastal State (when consistent with international law) concerning innocent passage and disregards any request for compliance made to it.4 The right of innocent passage is addressed in more detail in Chapter Three: Freedom of Navigation. Additionally, the LOSC provisions on protection and preservation of the marine environment do not apply to warships.5

Defining Immunity

In accordance with U.S. policy and the U.S. interpretation of international law regarding sovereign immunity, full sovereign immunity means immunity from arrest and search in national or international waters, foreign taxation, foreign state regulation requiring flying the flag of foreign State, and exclusive control over persons and acts performed on onboard.6 Sovereign immune vessels cannot be required to consent to onboard search or inspection, and police and port authorities may only board with permission of the commanding officer or master. Sovereign immune vessels shall not be required to fly a host nation’s flag in port or when transiting a territorial sea. Regarding taxes and fees, if port authorities or husbanding agents attempt to assess fees such as a port tax, port tariff, port marine pass, or tolls on vessels with sovereign immunity, the vessel’s captain should request an itemized list of all charges and explain that sovereign immune vessels cannot be charged port fees. However, they may pay for all goods and services provided by port authorities. It is the policy of the U.S. to never provide individual health records and to never allow health or sanitary inspections. However, captains must comply with quarantine regulations and restrictions for the port where the sovereign immune vessel is located. The U.S. does not provide crew lists to host nation authorities under any circumstances with no distinction made between military and non-military personnel. In response to a request for a crew list, captains should inform the host nation that the U.S. policy prohibits them from complying with this request.

U.S. Policy on Sovereign Immunity for Warships and Naval Auxiliaries

It is the policy of the U.S. to assert the privilege of sovereign immunity for all United States Ship (USS) vessels and small craft. USS vessels include, but are not limited to: U.S. Naval Ships (USNS), U.S. Coast Guard Cutter vessels (USCGC), other vessels owned by the U.S., U.S. flagged bareboat and time-charter vessels, and voyage charter vessels for the duration of government service. Small craft include, but are not limited to: motor whale boats, landing craft air cushioned and all other small boats, and craft and vehicles deployed from larger sovereign immune craft. In addition to USS vessels and small craft, the U.S. asserts sovereign immunity for underwater unmanned systems (UUS) and underwater unmanned vehicles (UUV) engaged exclusively in governmental, non-commercial service. How a small craft is launched has no bearing on its status. Sovereign immunity for both UUS and UUV systems may be considered an extension of the sovereign immune vessel or aircraft from which they were launched, or they may be considered entitled to sovereign immunity as naval auxiliaries.

The Military Sealift Command Policy

The Military Sealift Command (MSC) is the provider of ocean transportation for the U.S. Navy and the Department of Defense (DoD). It is a critical element of U.S. maritime security and supports many naval operations. MSC vessels include:

  • U.S. naval vessels assigned to MSC;
  • U.S. Maritime Administration’s National Defense Reserve Fleet (NDRF) and its Ready Reserve Force (RRF) when activated and assigned to MSC;
  • Privately-owned vessels under time charter to MSC with the Afloat Prepositioned Force (APF); and
  • Vessels chartered by MSC for a period of time or under MSC charter for a specific voyage or voyages.

The APF consists of ships loaded with combat equipment and support items located near potential trouble spots for quick deployment. It is U.S. policy to not only assert the full privileges of sovereign immunity for all MSC vessels owned by the U.S., but also for MSC time and voyage chartered ships in the APF. For MSC time and voyage chartered ships not in the APF, the U.S. only asserts freedom from arrest or taxation, but reserves the right to assert full sovereign immunity on a case-by-case basis. As a matter of policy, the U.S. does not claim sovereign immunity for MSC foreign-flagged voyage or MSC foreign-flagged time chartered vessels.

Although MSC vessels owned by the U.S., and U.S. flagged vessels bareboat or time chartered by the MSC are not to provide crew lists to foreign authorities, the Master may provide a shore party list for crew members going ashore to the host nation if requested. The list may contain only the names and passport numbers of those personnel and must not include health records, job descriptions, or employers. Masters must also comply with applicable agreements between the U.S. and the host nations, such as Status of Forces Agreements (SOFA), that specify procedures for port visits to the host nation.

Limited privileges of sovereign immunity for MSC U.S.-flagged voyage-charter vessels look quite different from full sovereign immunity. In the absence of an order to assert full sovereign immunity, vessels may provide crew lists to foreign authorities as a condition of port entry or to satisfy local immigration requirements similar to commercial vessels. Foreign authorities may search MSC U.S.-flagged charted vessels, but masters must deny requests to search U.S. military cargo.7

U.S. Position on Sovereign Immunity for Military and Auxiliary Aircraft

In accordance with Article 3 of the Convention on International Civil Aviation, military aircraft are considered State aircraft, and therefore also enjoy sovereign immunity from search and inspection.8 Foreign officials are only allowed to board the aircraft with the consent of the aircraft commander. Although military aircraft are generally not allowed to enter the national airspace or land of the sovereign territory of another nation without authorization, this is subject to the rights of transit passage, archipelagic sea-lane passage, and assistance entry. Additional information about these rights can be found in Chapter Three: Freedom of Navigation. Aircraft commanders must certify compliance with local customs, immigration, or quarantine requirements, or the aircraft may be directed to leave the territory and the national airspace of a State.

Auxiliary aircraft owned and under the exclusive control of the armed forces are considered State aircraft. The designation of State aircraft can be applied to civilian owned and operated aircraft if contracted by the DoD and used in military service. If designated as State aircraft, auxiliary aircraft enjoy sovereign immunity from search and inspection. As matters of policy, Air Mobility Command-charter aircraft are not designated as State aircraft. However, unmanned aerial vehicles (UAV) and remotely piloted vehicles are generally considered to be military aircraft. As such, they enjoy the same navigational rights and protections of applicable domestic and international law as manned aircraft.



  1. The Schooner Exch. v. McFaddon, 11 U.S. (7 Cranch) 116 (1812) (under international custom jurisdiction was presumed to be waived in a number of situations).
  2. United Nations Convention on the Law of the Sea, Article 29, Dec. 10, 1982, 1833 U.N.T.S. 397 [hereinafter LOSC]. (available at:
  3. LOSC, Articles 95-96.
  4. LOSC, Articles 30-32.
  5. LOSC, Article 236
  6. U.S. Navy, U.S. Marine Corps & U.S. Coast Guard, NWP 1-14M/MCWP 5-12.1/COMDTPUB P5800.7A, The Commander’s Handbook on the Law of Naval Operations (2007); OFFICE OF THE CHIEF OF NAVAL OPERATIONS, NAVADMIN 158/16, SOVEREIGN IMMUNITY POLICY (available at (This is a valuable resource on US policy regarding sovereign immunity questions generally).
  7. U.S. Navy, U.S. Marine Corps & U.S. Coast Guard, NWP 1-14M/MCWP 5-12.1/COMDTPUB P5800.7A, The Commander’s Handbook on the Law of Naval Operations (2007); OFFICE OF THE CHIEF OF NAVAL OPERATIONS, NAVADMIN 158/16, SOVEREIGN IMMUNITY POLICY (available at (This is a valuable resource on US policy regarding sovereign immunity questions generally).
  8. LOSC, Article 236
  9. Convention on International Civil Aviation, art. 3, Dec. 7, 1944, 15 U.N.T.S. 295.