General principles on the use of force and their application at sea

Articles 2(4) and 51 of the UN Charter and the customary international law Caroline Principles govern the use of force in international law. Despite these principles having a daily relevance in international relations, there remains considerable scope for debate about when a right of self-defence arises and how far it extends. So much depends upon the factual circumstances which amount to a threat, it is unsurprising that the law of self-defence is not a settled concept. It may be because it is always preferable to be the defender rather than the aggressor, and therefore to argue that a particular use of force is, or is not, an act of self-defence rather than an act of aggr ession. As Judge Schwebel noted in his dissent in the Nicaragua Case, ‘aggression can only be ultimately defined and found in the particular case in the light of its particular facts’.1 Given the inherent tensions in the concept of self-defence generally, it is unsurprising that its application at sea is also not settled. This chapter will consider a range of concepts in self-defence and their application at sea. It will look first at the principles enshrined in article 51 and also the Caroline Principles. It will then look at the cases that have applied these principles at sea - the Corfu Channel Case, the Nicaragua Case, the Saiga Case, the Oil Platforms Case and the South China Sea Arbitration. This chapter will argue that it is possible to derive some clear rules from these cases, even if they do not deal comprehensively or precisely with all of the relevant issues. Large areas of uncertainty remain about the lawful use of force in incidents at sea involving warships, and these areas will always remain so because of the inherent tensions in the concept of self-defence.


345 (Judge Schwebel) [n.b. page numbers will refer to those at the bottom of the page on the version published on the ICJ website, given that there is different page numbering at the top of the page] As to the uncertainty of the law see James Green, The International Court of Justice and Self-Defence in International Law (Hart, 2009) 143-144

The right to use force in general international law

Articles 2(4) and 51 of the United Nations Charter

Articles 2(4) and 51 of the United Nations (UN) Charter must be the starting point for any discussion of the use of force in international law, otherwise known as the jus ad belluni. (As opposed to the jus in bello which regulates conduct once an aimed conflict has commenced.)

Article 2(4) provides:

All members shall refrain in their international relations from the threat or use of force against the territorial integrity or political independence of any state, or in any other maimer inconsistent with the Purposes of the United Nations.

Notably, the Purposes of the United Nations set down in Article 1 of the Charter include maintaining ‘international peace and security’, preventing ‘breaches of the peace’, and developing ‘friendly relations’. The obligations of states under Article 2 do not allow room for the use of force beyond that authorised by the UN Charter, or in self-defence. Importantly, article 301 of the 1982 Convention reflects very similar wording:

In exercising their rights and performing their duties under this Convention, States Parties shall refrain from any threat or use of force against the territorial integrity or political independence of any State, or in any other maimer inconsistent with the principles of international law embodied in the Charter of the United Nations.

Article 51 of the Charter addresses self-defence and provides:

Nothing in the present Charter shall impair the inherent right of individual or collective self-defence if an armed attack occurs against a Member of the United Nations, until the Security Council has taken measures necessary to maintain international peace and security.

Measures taken by Members in the exercise of this right of self-defence shall be immediately reported to the Security Council and shall


See Myron Nordquist, Satya Nandan and Shabtai Rosenne (eds), United Nations Convention on the Law of the Sea: Commentary Online, 'Article 87: Freedom of the High Seas’, 72,85, ‘Article 88: Reservation of the High Seas for Peaceful Purposes’, 87, 89-91 and ‘Article 301: Peaceful Uses of the Seas’, 153; discussed in James Kraska, Maritime Power and the Law of the Sea (Oxford University Press, 2011) 255-256

General principles on the use of force 15 not in any way affect the authority and responsibility of the Security Council under the present Charter to take at any time such action as it deems necessary in order to maintain or restore international peace and security.

This article needs some interpretation in order to apply it at sea. It is concerned with armed attacks against member states and requires members to report measures taken in self-defence to the Secmity Council immediately. To apply at sea, an armed attack on a member must be presumed to include an armed attack on warships or other vessels flying the flag of a memberstate, and measures in self-defence involving warships may need to be reported to the Secmity Council.

It is important to emphasise at this point that article 51 srrpplements, rather than supplants customary international law. As the International Court of Justice stated in the Nicaragua Case:

The Court therefore finds that Article 51 of the Charter is only meaningful on the basis that there is a ‘natural’ or ‘inherent’ right of self-defence, and it is hard to see how this can be other than of a customary' nature, even if its present content has been confirmed and influenced by the Charter. Moreover the Charter, having itself recognized the existence of this right, does not go on to regulate directly all aspects of its content. . . . Customary international law continues to exist alongside treaty law?

It is therefore essential to consider the customary international law of self-defence, particrtlarly in its application at sea.

The Caroline Principles

The Caroline Principles are often cited as defining the customary' international rules on self-defence. They allow for an exercise of the right of self-defence where there is an ‘instant and overwhelming necessity for self-defence leaving no choice of means and no moment for deliberation’. That the incident which gave rise to them involved an attack against a ship is helpful in making the principles more practically focussed.

Tire operative words derive from a letter from the US Secretary of State to the British Foreign Secretary, inviting a justification for the use of force in

3 Nicaragua Case 84

the incident. In notes covering the correspondence between the two secretaries, Hunter Miller explained the factual circumstances as follows:

During the insurrection in Canada in 1837 sympathetic commotions occurred at various places in the United States, especially along the Canadian border. The Government of the United States adopted active measures for the enforcement of the neutrality laws, but the difficulties of the situation were increased by the course of the insurgents, who, when defeated, sought refuge in the United States, where they endeavored to recruit their forces.

On the 28th of the month, the United States marshal for the northern district of New York, who had proceeded to Buffalo for the purpose of suppressing violations of neutrality, reported that he had found 200 or 300 men, mostly from the American side of the Niagara River, encamped on Navy Island, in Upper Canada, aimed and under the command of ‘General’ Van Rensselaer, of Albany, and that the encampment had received accessions till it numbered about 1,000 men, well aimed. . . . There was also an encampment at Black Rock.

On the 29th of December occurred the destruction of the Caroline. This vessel was a small steamer employed by the men at Black Rock and on Navy Island in communicating with the mainland. ... At midnight about 70 or 80 armed men boarded the steamer and attacked the persons on board with muskets, swords, and cutlasses. The ‘passengers and crew’, of whom there were in all 33, merely endeavored to escape. After this attack the assailing force set the steamer on fire, cut her loose, and set her adrift over the Niagara Falls.

The United States accepted the British explanation, and apology, as follows:

Undoubtedly it is just, that while it is admitted that exceptions giowing out of the great law of self-defence do exist, those exceptions should be confined to cases in which the ‘necessity of that self-defence is instant, overwhelming, and leaving no choice of means, and no moment for deliberation’.

Understanding these principles alike, the difference between the two Governments is only whether the facts in the case of the ‘Caroline’ make out a case of such necessity for the purpose of self-defence . . . seeing, finally, that it is now admitted that an explanation and apology


Hunter Miller (ed), Treaties and Other International Acts of the United States of America: 1836-1846 (Government Printing Office, Washington, 1934) Vol 4, Documents 80-121; see Green, n 1, 64-76

for this violation was due at the tune, the President is content to receive these acknowledgments and assurances in the conciliatory spirit.5

Whilst the correspondence is not normally quoted at such length in scholarship on the use of force in international law, it is worth doing so because it can be seen that the attack on the Caroline was in response to a serious, but not immediate, threat.

The immediacy of the threat was in issue in both the Corfu Channel Case and also the Oil Platforms Case, as discussed subsequently Whilst not having the binding effect of Security Council Resolutions, two key General Assembly Resolutions inform the cases on this issue, so it is important to address them before turning to the cases.6

General assembly resolutions

XXV- Declaration on Principles of International Law concerning Friendly Relations and Co-operation among States in accordance with the Charter of the United Nations of 19707

This resolution has a terrestrial focus on non-intervention in the context of the decolonisation process but its statement with respect to not aggravating disputes is significant for maritime incidents:

States parties to an international dispute, as well as other States shall refrain from any action which may aggravate the Situation so as to endanger the maintenance of international peace and seciuity, and shall act in accordance with the purposes and principles of the United Nations.8

As Chapter 6 will discuss, this principle has informed obligations on states in relation to disputed waters not to aggravate the dispute through the use of forcefill measures.

  • 5 Ibid.
  • 6 e g. the Court in Nicaragua 91:

In determining the legal rale which applies to these latter forms, the Court can again draw on the formulations contained in the Declaration on Principles of International Law concerning Friendly Relations and Co-operation among States in accordance with the Charter of the United Nations (General Assembly resolution 2625 (XXX'), referred to above). As already observed, the adoption by States of this text affords an indication of their opinio juris as to customary international law on the question. [The Court then quotes the resolution at length]

  • 7 UN Doc. A'RES/25/2625 (24 October 1970)
  • 8 Ibid.

XXIX - Definition of Aggression of 197fi

The Definition of Aggression resolution makes the critical point about the first use of force which is the central challenge that this book seeks to address:

Article 2

The first use of armed force by a state in contravention of the Charter shall constitute prima facie evidence of an act of aggression although the Security Council may, in conformity with the Charter, conclude that a determination that an act of aggression has been committed would not be justified in the light of other relevant circumstances, including the fact that the acts concerned or then consequences are not of sufficient gravity.[1]

Article 2 quite clearly reflects the problem with being perceived as the aggressor. This problem pervades incidents involving warships below the level of armed conflict, where no party wishes to be seen as the aggressor. The risk in any miscalculation in the use of force involves not only the consequences of death, injury and damage but also the loss of sympathy and support that could come with the opprobrium of being an aggressor.11

Notably, article 2 also leaves room for an action to be not of sufficient gravity to be an act of aggression. Chapter 2 will address the threshold of gravity and its consequences for whether a matter is one of unit or national self-defence: whether it crosses the threshold for the application of the law of armed conflict and even the application of the military activities exemption from the jurisdiction of the International Tribunal for the Law of the Sea.

Further, it is worth noting that the Definition of Aggression is not entirely focussed on terrestrial matters, including the following as acts of aggr ession:

Article 3

(b) Bombardment by the armed forces of a State against the territory of another State or the use of any weapons by a state against the territory of another state;

  • (c) The blockade of the ports or coasts of a state by the armed forces of another state;
  • (d) An attack by the aimed forces of a state on the land, sea or air forces, or marine and air fleets of another state;
  • (e) The use of aimed forces of one state which are within the territory of another state with the agreement of the receiving state, in contravention of the conditions provided for in the agreement or any extension of their presence in such territory beyond the termination of the agreement.

Whilst bombardment and blockade may be rather obvious forms of aggression, paragraph (d) refers to uses of force that may potentially be at quite a low level. This is significant in light of the Oil Platforms Case discussed subsequently and the threshold for the application of the law of aimed conflict discussed in Chapter 3. Paragraph (e) could include situations where the presence of foreign warships in internal waters, or even the territorial sea, is no longer in compliance with the diplomatic clearance authorising that presence. That this could amount to aggression in deliberate and menacing situations is also significant. It is an issue to which Chapter 4 will mm. It important first to see the application of these principles in the cases.

  • [1] 2 As to the customary international law status of the Resolution see ibid. 93; also it has become the basis of the crime of aggression under article 8 bis of the Rome Statute of the International Criminal Court (opened for signature 17 July 1998) 2187 UNTS 3 (entered into force 1 July 2002) 3 Judge Schwebel in his dissent in the Nicaragua Case provides both a critique of the Definition of Aggression whilst accepting its significance for customary international law, 345
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