Lieber Studies Indo-Pacific Volume – Interpretative Choice and Risk in Indo-Pacific Air Domain Challenges
Editors’ note: This post is based on the author’s chapter in Armed Conflict and International Law in the Indo-Pacific Region (Douglas Guilfoyle & Jennifer Maddocks eds. 2026), the thirteenth volume of the Lieber Studies Series published with Oxford University Press.
Legal challenges in the Indo-Pacific air domain have typically been overshadowed by legal issues arising in, under, and from the sea. Yet resolution of many of these challenges remains dependent on the appetite for risk in the law governing maritime operations.
Australia’s recent National Defence Strategy is based on deterrence through denial, and places an important emphasis on long-range strike capabilities. This highlights one particular problem. Looking at the map, the major archipelagic States of Indonesia and the Philippines, and with them Papua New Guinea and Fiji, lie directly to Australia’s north in a more or less contiguous band. Current interpretative approaches would not clearly permit long-range missiles to exercise archipelagic sea lanes overflight in the airspace of these States. As a result, if these States were neutral in some future conflict involving Australia, then missiles designed primarily as anti-access area denial (A2AD) systems may ironically be constrained by norms of access.
There are, of course, interpretative choices in the laws of air and sea that could be made to address this situation, each with risks that could impact other aspects of maritime access.
Language and Choice in Treaty Interpretation
The development of treaty language is a clear process of choice and negotiation between States. Once a treaty is adopted, its language remains fixed. However, the social, political, economic, and cultural contexts of its application are in “constant flux.” Treaty terms may need to apply to new circumstances, their ordinary meaning may change over time, or subsequent interpretative practice can develop the way terms are applied.
The International Court of Justice (ICJ) has intermittently relied on evolutive interpretation, which it draws from the intent of treaty drafters. In Construction of a Road in Costa Rica along the San Juan River, the court allowed such interpretation of “generic” terms because the parties’ intent “was, or may be presumed to have been, to give the terms used—or some of them—a meaning or content capable of evolving, not one fixed once and for all, so as to make allowance for, among other things, developments in international law.”
Missiles, Aircraft and Archipelagic Sea Lanes Overflight of Neutral States
The problem highlighted by Australia’s National Defence Strategy is best illustrated with a case study. The UN Convention on the Law of the Sea (UNCLOS) creates a non-suspendable right of passage and overflight through archipelagic waters, including for warships and military aircraft, on the routes normally used for international navigation. When in archipelagic sea lanes passage (ASLP), warships and military aircraft shall proceed without delay and in normal mode, refraining from any threat or use of force against the archipelagic State.
If the archipelagic State declares itself neutral during armed conflict, a strong position has been taken that ASLP rights continue to apply to belligerent warships and military aircraft, notably in the San Remo Manual. This is the logical consequence of the non-suspendability of peacetime ASLP, although it has not been tested in practice and UNCLOS itself does not address the issue of armed conflict directly. Rule 172(a)(ii) in the Manual on International Law Applicable to Air and Missile Warfare (the HPCR Manual) adopts the San Remo position for the air domain, without detailed analysis.
If a missile is interpreted to be a military aircraft, then as a starting point it would have access to ASLP overflight of a neutral State, without needing consent or another justification such as self-defence. UNCLOS offers no definition of an aircraft, and the HPCR Manual simply applies the definitions in Annex 7 of the Chicago Convention to armed conflict. However, in a classic textual argument, Simon Lindsay has recently demonstrated that, despite their capacity for navigation, modern missile systems are best considered weapons and not military aircraft for ASLP purposes.
There is a potential alternative. Could an evolutive approach be taken to the definition of military aircraft? After all, the current era of unmanned aerial combat vehicles is vastly changed compared to capabilities in 1944. The future may hold other yet uncontemplated developments in terms of military objects capable of air navigation. Further, “aircraft” is the kind of generic term for which the ICJ has accepted evolutive approaches. There are legal technical challenges in the argument, including,
– whether the UNCLOS drafters intended “aircraft,” and “military aircraft” as a subset, to have an evolutive meaning may be difficult to answer from available records, given the consensus-driven decision-making of the treaty conferences.
– re-interpreting the Chicago Convention in the first instance, then “reading it across” to UNCLOS offers better logic, but goes beyond the ICJ’s limited jurisprudence, which deals mainly with self-contained bilateral agreements.
Second, there is the requirement that ASLP should not threaten the archipelagic State. Is mere overflight of an archipelagic sea lane unlawfully threatening? There is potentially relevant practice in connection with the non-suspendable right of transit passage in U.S. Operation El Dorado Canyon in 1986. During this operation, U.S. F-111s departed from British bases and overflew the Strait of Gibraltar to conduct strikes on Libya, despite Spain in particular refusing cooperation and access to national airspace for the flight.
The immediate risk is consequential. If one makes the case for evolutive interpretation to bring missile overflight within ASLP, the intent of the drafters is critical. This includes the intent of specially affected States, which may raise different perspectives. Indonesia is a case in point.
The Influence of History in the Indonesian Archipelago
The peoples of the Indonesian archipelago and neighbouring States are part of an historical maritime zone, in which political, cultural, and economic relationships were primarily engaged on a maritime basis. The history of the archipelago is distinguished by successive thalassocracies, or “sea power states” in which “constructed national identity” was maritime in nature and the State was dependent on the sea, distinct from Mahan’s approach to sea power as national strategy. This has resulted in a particular conception of the sovereign relationship between land and sea.
In the Indonesian archipelago, Srivijaya was the first maritime-trade-based empire to emerge (7th-11th centuries), followed by the Majahapits (13th to 16th centuries), the Sultanate of Brunei (peaking in the 16th century but continuing), the Bugis peoples (17th-18th centuries), the Temengongs of Singapore and the Sultanate of Sulu (18th-19th centuries). Some rulers drew support from other archipelagic maritime peoples, particularly Iranun raiders from Mindanao, and the Iban of Borneo.
The second key historical point is the sensitivity of transit access over regional maritime interests. For a millennium, external powers were primarily concerned with trade and navigational access, rather than colonization. Chinese maritime engagement dates to the 12th and 13th centuries. The advent of European powers in the 16th century added competition, as the Portuguese, Dutch, and British successively attempted to control the regional spice trade and sea routes to China.
Thirdly, and in a connected point, the arrival of European sea powers seeking control of navigational routes meant the introduction of law as a means of moderating competitive access. For the British and Dutch in particular, control of maritime access was justified as legitimate by using the concept of “piracy” to exclude and target archipelagic peoples.
These interconnected themes continue to shape Indonesia’s approach, coalescing into the national doctrine of wawasan nusantara. Developed as Indonesia sought to draw together thousands of islands and hundreds of peoples into a single State after 1945, this concept uses the sea as the unifying point. Wawasan nusantara has been described as the “fundamental standpoint of Indonesian geopolitics.” In this “archipelagic vision” of Indonesian statehood, “the water between the islands must become the connectors rather than separators.” Recent strategy for a “blue Pacific continent” among Pacific island States also points to a concept of the maritime domain as a national unifier, rather than a space between territory through which freedom of passage for others is paramount.
This history is important. Indonesia was a chief advocate for inclusion of the concept of archipelagic States in UNCLOS. Although it did agree to non-suspendable passage rights in the final treaty text, wawasan nusantara remains a cornerstone of Indonesia’s interpretative approach. Recent Indonesian commentary, for example, has suggested that the passage of AUKUS nuclear-powered submarines should be prohibited as inherently threatening to Indonesian sovereignty. Re-opening discussion to evolutive interpretation of military air passage could potentially lead to a revised understanding of archipelagic “sovereignty” and of prohibited threats to it in the exercise of ASLP.
There are alternative legal arguments for missile overflight which are beyond the scope of this post. For example, Charter self-defence could apply as an exception to the control of archipelagic overflight in UNCLOS. Operation El Dorado Canyon may lend some support to this, although it would not permit broader use of long-range strikes in conflict. As for maritime neutrality, there may be a developing nuance of “qualified neutrality,” in which a neutral State can provide limited support to a State subject to unlawful aggression by another, but this could amount to a consent-based passage regime at odds with ASLP.
Conclusion
Access and overflight are chief among Indo-Pacific air domain challenges, particularly if one or more archipelagic States remain neutral in any future armed conflict. Current textual views of the law would exclude the free overflight of long-range strike capabilities via the archipelagic sea lanes of neutral States. While evolutive approaches might foster wider access, they could also open other aspects of the archipelagic regime to evolutive interpretation. Archipelagic States, with a different maritime history and no previous involvement in the development of these maritime/air rules in case of neutrality, may favour development in new or unexpected ways.
To reduce future risk, including the risk of failure to gain air superiority during any future conflict, the legal analysis must consider the strategic balance of interpretative choice and risk now, maintaining throughout the commitment of all sovereign States to good faith in the performance of their legal obligations.
***
Air Commodore Angeline Lewis is a senior legal officer in the Royal Australian Air Force.
The views expressed are those of the author, and do not necessarily reflect the official position of the United States Military Academy, Department of the Army, or Department of Defense.
Articles of War is a forum for professionals to share opinions and cultivate ideas. Articles of War does not screen articles to fit a particular editorial agenda, nor endorse or advocate material that is published. Authorship does not indicate affiliation with Articles of War, the Lieber Institute, or the United States Military Academy West Point.
Photo credit: U.S. Air Force, Tech. Sgt. Amy Lovgren
