Proportionality and the threshold of armed conflict
How far does the right of self-defence extend? Is it only to the point that an attacker has simply turned away or ceased firing, or is it until after they have clearly left the scene? Does the right extend to using force against the place the attack was launched from, whether a base or mothership, or against supporting vessels or aircraft that may be surveilling, reporting or controlling? The first two chapters primarily dealt with when force may be used. This chapter focusses more on the question of how much force may be used and for how long, and against whom. The operational effect of the answers to these questions is quite profound in terms of the intensity of any engagement. The requirement of proportionality, and the unit self-defence approach effectively taken in the cases, together limit the use of force to the immediate defence of the warship or shore installation. It does not extend to targets which do not pose an immediate threat. In particular the law of aimed conflict does not apply as readily as some manuals would suggest, meaning that an attack on or by a warship does not automatically mean that it is lawfill to target units of an opposing force which do not pose a threat.
The question of how much force to use and for how long is the issue of proportionality in the use of force. This is a highly contextual problem, although the cases provide some guidance. The Corfu Channel Case made clear that British warships could not sweep the channel of mines, in order to prevent further mine strikes, on the basis that this was not consistent with the right of innocent passage in the territorial sea of Albania.1 (Chapter 4 will consider whether this conclusion would be any different under the regime of transit passage through an international strait.) Importantly, the
Corfu Channel Case 36
case also made clear that the British warships could proceed through the strait at action stations, that is to say, ready to use force at a moment’s notice in order to defend themselves. The ships’ guns were trained fore and aft, so the external appearance of the ships did not suggest that they were ready to shell the Albanian shore batteries. The ships had orders to do so if fired upon, however, and the Court did not object. Altogether this suggests a view that the ships could be very forceful in their immediate response to an attack, but such action in self-defence was limited both in time and space. Any exercise of force was limited to the time period of the passage and to the immediate source of the threat, that is the shore batteries and not other targets. It could not occur later to prevent a future attack. It could not be anything more than a response to an attack occurring at the time.
In a somewhat similar way, the Oil Platforms Case also rejected the idea of a self-defence response occurring well after the actual passage takes place.
Therefore, in order to establish that it was legally justified in attacking the Iranian platforms in exercise of the right of individual self-defence, the United States has to show that attacks had been made upon it for which Iran was responsible; and that those attacks were of such a nature as to be qualified as ‘armed attacks’ within the meaning of that expression in Article 51 of the United Nations Charter, and as understood in customary law on the use of force. .. . The United States must also show that its actions were necessary and proportional to the armed attack made on it, and that the platforms were a legitimate military target open to attack in the exercise of self-defence.
This passage is notable for two particular reasons. The first is that the Court established that, for the United States to target the oil platforms, the attack to which it was responding had to amount to an aimed attack upon the United States. It did not see that attacking the oil platforms could have occurred m response to a use of force by Iran below that threshold. This could mean that unit self-defence has to be equated to national self-defence. Alternatively, and more consistently with the Corfu Channel Case reasoning, a US response that was not a response to the immediate threat to shipping, as m this case occurring some days later, could only be justified as an act of national self-defence. In this case it was not. This is a preferable view in that it limits the scope for the use of force to the immediate defence of a unit.
The other interesting point is the use of the term ‘legitimate military target’. This is close to the language of the law of aimed conflict. It is not language just concerned with targets posing an immediate threat to US ships, but rather with a slightly broader notion of national self-defence. It will be relevant to the subsequent discussion of the thr eshold of application of the law of armed conflict.
As to the requir ements of proportionality more generally, in the Nicaragua Case, Judge Schwebel (in dissent) quoted Judge Ago at length from a report on State Responsibility to the International Law Commission:
Moreover, for the test of proportionality to be met, there by no means must be perfect proportionality. As Judge Ago has rightly written: ‘The requirement of the proportionality of the action taken in self defence . . . concerns the relationship between that action and its purpose, namely . . . that of halting and repelling the attack. It would be mistaken, however, to think that there must be proportionality between the conduct constituting the armed attack and the opposing conduct. The action needed to halt and repulse the attack may well have to assume dimensions disproportionate to those of the attack suffered. What matters in this respect is the result to be achieved by the ‘defensive’ action, and not the forms, substance and strength of the action itself.... Above all, one must guard against any tendency in this connection to consider, even unwittingly, that self-defence is actually a form of sanction, such as reprisals. .. . But in the case of action taken for the specific purpose of halting and repelling an armed attack, this does not mean that the action should be more or less conunensurate with the attack... .
Judge Ago adds ‘There remains the third requirement, namely that armed resistance to armed attack should take place immediately, i.e., while the attack is still going on, and not after it has ended. A State can no longer claim to be acting in self-defence if, for example, it drops bombs on a country which has made an armed raid into its territory after the raid has ended and the troops have withdrawn beyond the frontier. If, how'ever, the attack in question consisted of a number of successive acts, the requirement of the immediacy of the self-defensive action would have to be looked at in the light of those acts as a whole.
At all events, practice and doctrine seem to endorse this requirement.
There are three points in this quote which warrant closer attention. The fir st is that proportionality does not mean equivalence. Proportionality in jus ad belluni terms concerns that which is required to halt and repel the attack. It is not using the exactly the same amount of force in defence in reply to an attack. The second point is the emphasis on self-defence not amounting to a reprisal, which means that the response must be immediate and directly in response to the attack. This is consistent with the reasoning in both the Corfu Channel Case and also the Oil Platforms Case. The last point is a new aspect of this discussion, bitt an important one. That is that a self-defensive action can be seen in the context of a series of attacks. This was significant in both the Corfu Channel Case and the Oil Platforms Case, where the incidents in question occurred in the context of ongoing uses of force. In neither case did this context pennit an extended or delayed response to the attacks, whether the clearing of the minefield or the attacks on the platforms, but it could have gone to the question of the hostile intent of a threatening unit.
This is perhaps best illustrated by example. A single attack by an aircraft or a vessel might be said to have finished when it turns away and departs the area. Arguably, the need to repel the attack no longer exists and force may no longer be used. Pursuing the attacker and using force against it may be unlawfirl, even amounting to a reprisal. On the other hand, if such an attack forms part of a pattern of repeated behaviour, arguably then, force may be used sooner, perhaps as soon as an attacker is sighted, rather than waiting for other indicia of an attack. Force may also be used later. Turning away and leaving the area may simply be a tactic or a manoeuvere in advance of a further attack. The pursuit and use of force against the attacking vessel or aircraft may then be justified.
A further question arises then as to whether it is lawful to target the place from which the attacks are launched, whether a base, airfield, mothership or offshore facility for example. In the case of a single attack this may be very difficult to justify. Separation in time and space from the attack would probably place such a response beyond the limits indicated in both the Corfu Channel Case and the Oil Platforms Case. Should there be a series of attacks, however, using force against the place from which they are launched might meet the test of the Caroline Principles through an ‘instant
Proportionality 51 and overwhelming necessity for self defence leaving no choice of means and no moment for deliberation’. In the example of the British warships returning fire to Albanian shore batteries which fired upon them, were there an ongoing succession of attacks from such batteries, British warships may have engaged them as soon as they started to tram their guns but before they had even fired. They may also have fired upon other shore batteries which had not yet themselves engaged in firing on the British warships. To do otherwise might lead to the destruction of the warship under attack, but only for so long as those warships were engaged in passage though the Corfu Channel and only in order to conduct their navigation though it.
In the example of the Gulf during the Tanker War, this may similarly have meant that US warships under fire from Iranian gunboats may have engaged all Iranian military targets within a range to inflict harm upon US units. This would be on the basis that, within the context of the Gulf at the time, it was reasonable to determine that filing on the part of one or some Iranian units was an indication of hostile intent on the part of all that were within range and also capable of inflicting harm upon US warships.
The separation in space and time between the attacks and the action in self-defence will be highly significant. Whether it is too much will also be highly contextual. It will depend on the extent to which it is arguable that the action in self-defence is necessary to prevent further attacks on the current passage of the warship. Once the warship is out of range of the place from which the attacks came, there should no longer be a need to use force against it. The question of what is a proportionate response leads into the question of the applicability of the law of aimed conflict, particularly the law of naval warfare.
-  Ibid. 31 2 Ibid. 3 Ibid. 27 4 Oil Platforms Case 27
-  e.g. the term ‘specific military objective’ in article 51 of the Protocol Additional to the Geneva Conventions of 12 August 1940, and Relating to the Protection of Victims of International Armed Conflicts (Additional Protocol I) adopted S June 1977 (1125 UNTS (1979) 3-608) entered into force 7 December 1978 2 Oil Platforms Case 367
-  Ibid. 2 See Royal Australian Navy Manual of International Law Australian Book of Reference (ABR) 5179 (1998) para 7.9, and the note which follows on the sinking of ARA General Belgrano.