Self-Defence and Maritime Interception in law of the sea, maritime law and customary international law

Self-defence as a legal basis for military operations has since the 9/11 attack been
under much scrutiny, in particular with regard to how this legal basis should be
applied in contemporary threats. In the maritime dimension self-defence is often
argued in two different contexts. It is firstly argued as the legal basis for the
deployment of large-scale military campaigns that, including a naval component.
Recent examples are Operations Enduring Freedom, Active Endeavour, Cast Lead
and Change Direction. Self-defence is also argued as a basis to stop weapons of
mass destruction and terrorists, or a combination thereof, at sea, outside the context
of large scale military campaigns. The latter approach applies the right of
self-defence against single threats in individual cases. This second approach has
particularly emerged since the fight against terrorists was broadened against persons
and cargo beyond Al Qaida, the Taliban and its affiliates. It was primarily initiated
by the US National Security Strategy (2002), in which the former US president
George W. Bush coined the much debated idea of pre-emptively countering threats
to US national security, in particular terrorists who obtain and use weapons of mass
destruction. Interestingly, back in 1956, the International Law Commission noted
on the issue of whether the right of self-defence could be another exception to the
exclusive jurisdiction of the flag State that it was not ‘deemed to be advisable’,
because of the vagueness of terms as ‘imminent danger’ and ‘hostile acts’, which
leaves them open to abuse. To some, the issue implied the recognition of the idea
itself. To others, the ILC-commentary closed the subject. Today, however, the
discussion of self-defence in relation to the exclusive jurisdiction over a vessel has
received new attention in the legal arena. This chapter analyses the right of
self-defence in relation to maritime interception operations. It will first start with a
brief introduction to the right of self-defence and remark on the application of self-defence through both large-scale military campaign naval operations in an interception role, and self-defence in response to single threats of WMD and

The Right of Self-Defence
Similar to the UN collective security system the legal basis of self-defence takes as
starting point the prohibition on the use of force laid down in Article 2(4) of the UN
Charter. The sources of the right of self-defence are usually considered to be based
on both the UN Charter and international customary law. These sources result in the
view that there are specifically written conditions for self-defence in Article 51 of
the UN Charter and additional conditions that are derived from customary international
law. Article 51 of the UN Charter reads as follows:
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 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.
The threshold condition that must be fulfilled in order to invoke the right of
self-defence is the existence of an armed attack. Once an armed attack exists the
reaction to the armed attack must fulfill the substantive customary conditions of
necessity, proportionality, and immediacy. Necessity relates to the existence of an
armed attack or an immediate threat of attack and focuses on the question whether
the use of force under self-defence is a measure of last resort to which there are no
other means or alternative available than the use of force. Proportionality focuses on
a balanced response to the armed attack, against the background of the purpose of
self-defence. This purpose is to halt and repel the attack, and, to some authors, also
includes ensuring that the attacker cannot mount future attacks. Immediacy considers
the temporal link between the attack and the start of the reaction to the attack
once the attack has occurred.
The answer to the question whether an armed attack has occurred, has been part
of extensive legal debate since the 9/11 attacks, in particular from a material,
temporal and personae perspective. These three perspectives deal with the questions
of what amounts to an armed attack, at what moment in time can the right of
self-defence be invoked and against whom can it be invoked. The debates have concentrated on whether self-defence could exist in an anticipatory manner, whether it can be invoked against non-state actors and which scale and effect the attack must have be to be considered an armed attack. This is not the place to extensively
repeat those debates, but it generally appears that, although the jurisprudence of the
ICJ is more reluctant, scholars are moving into the direction that the general
answer to the first two questions relating to the expanding scope of self-defence
might well be a positive one. Indeed an evolution in thought appears to have taken
place with regard to the scope of the armed attack, which now more readily considered
to include anticipatory attacks and attacks mounted by non-state actors. As
Van Steenberghe has concluded om the latter based on a study of recent state
practice; ‘…the interpretation of recent state practice amounts to considering that
the latter evidences a clear tendency towards allowing States to act in self-defence
in response to attacks, even if these attacks are committed only by non-state
actors’. In relation to self-defence in the context of maritime interception operations,
this evolution of thought opens the possibility to act against non-state actors
that are on board a vessel or use the vessels as an instrument in an armed attack. The
material aspect of self-defence emerges as an issue in the context of attacks against
warships and the possibilities a State and the individual warship commander might
have to react against it. But more importantly, the broadened scope of
self-defence in the temporal aspect is particularly of interest for proponents of the
view that foreign-flagged vessels that pose an imminent threat by virtue of
threatening cargo can be boarded based on self-defence. In this context anticipatory
self-defence, which is seen through the now generally accepted Caroline-criteria—
the armed attack must be instant, overwhelming, leaving no choice for other means,
and no moment for deliberation—12and the interpretation of immediacy is of
importance. Anticipatory self-defence in essence questions whether a State can act when the use of force against the State is about to happen and whether a State needs
to wait until an actual attack has occurred.

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