Could Indonesia Block Foreign Nuclear Subs at Maritime Choke Points?

Would it be permissible under international law to deny access of foreign nuclear-powered submarines through archipelagic sea lanes?

A U.S. Navy warship transits the Strait of Malacca, 2017 (USN file image)
A U.S. Navy warship transits the Strait of Malacca, 2017 (USN file image)

Published Mar 26, 2023 5:05 PM by The Lowy Interpreter

[By Dita Liliansa]

Indonesia, a nation that controls vital maritime chokepoints, finds itself at the epicentre of an unfolding geopolitical drama. As rivalry builds between the United States and China, the prospect of more nuclear submarines passing through Indonesian waters – including plans for AUKUS boats under the newly formed pact between Australia, the United Kingdom and the United States – brings an underlying legal question into focus.

All ships, including submarines, have guaranteed rights under the 1982 United Nations Convention on the Law of the Sea (UNCLOS), which Indonesia is a party to, to navigate through archipelagic waters under the right of “innocent passage” or the right of “archipelagic sea lanes passage”. The right of archipelagic sea lanes passage grants all ships the right to navigate continuously and expeditiously in their “normal mode” through archipelagic waters and the adjacent territorial sea. Submarines may navigate submerged since that is their normal mode of passage. This right “cannot be impeded or suspended” by the archipelagic state for any purpose. An archipelagic state may designate sea lanes through its archipelagic waters, but all normal routes used for international navigation must be included. If such a designation has not occurred or is considered a partial designation, the right of archipelagic sea lanes passage may be exercised through the routes normally used for international navigation.

While it is true that foreign nuclear-powered ships exercising the right of innocent passage are subject to stricter requirements under UNCLOS, the intention is not to limit passage.

Outside of archipelagic sea lanes, all ships are entitled to the more limited right of innocent passage throughout archipelagic waters and through the territorial sea. Submarines exercising the right of innocent passage must navigate on the surface and show their flag, and comply with other rules on innocent passage, such as refraining from engaging in any activity that is prejudicial to the peace, good order or security of the coastal state. An archipelagic state may “temporarily suspend the right of innocent passage” for foreign ships in specified areas of its archipelagic waters and territorial sea if such suspension is essential for the protection of its security, after providing due notice.

Statements by some Indonesian government officials in the wake of the AUKUS announcements suggest that Indonesia should consider prohibiting the passage of foreign submarines through its archipelagic waters if they are engaged in activities related to war or preparation of war or non-peaceful activities. While UNCLOS promotes peaceful uses of the seas and oceans, it contains no provision permitting archipelagic states to suspend the right of archipelagic sea lanes passage through their archipelagic waters. Rather, it specifically provides that there shall be no suspension of the right of archipelagic sea lanes passage.

While it is true that foreign nuclear-powered ships exercising the right of innocent passage are subject to stricter requirements under UNCLOS, such as carrying appropriate documents and complying with special precautionary measures established by international agreements, the intention is not to limit passage, but rather to guarantee that hazardous activities are effectively managed in line with international standards.

UNCLOS makes no exception to the passage rights of submarines based on their intended use or purpose. It only requires that the passage of submarines is in conformity with the provisions in UNCLOS. Even if there is an ongoing war, archipelagic states have an obligation to respect the right of archipelagic sea lanes passage of foreign submarines.

Some debate has arisen as to whether the provisions in UNCLOS are applicable during an international armed conflict. Views vary from UNCLOS not applying at all to UNCLOS remaining applicable. A moderate position suggests that the maritime rights and duties that states enjoy in peacetime continue with minor exceptions during an armed conflict.

In wartime, the law of naval warfare is considered the lex specialis regime that supersedes UNCLOS “for belligerent parties”. However, UNCLOS continues to govern the conduct between neutral and belligerent states, and among neutral states. This principle applies in particular to passage rights of foreign ships, including the rights of archipelagic sea lanes passage and innocent passage through archipelagic waters. The law of naval warfare thus modifies the relationship between neutral and belligerent states to some degree to ensure that neutral states are not harmed by the conflict and to prevent the conflict from escalating.

The law of naval warfare has evolved over time and is primarily based on customary international law. A series of conventions have been adopted to regulate naval warfare, but not all have been widely accepted. The San Remo Manual, prepared by a group of legal and naval experts, provides the most detailed and current rules for the conduct of naval warfare. While it is an unofficial statement, it appears to be widely accepted as a reflection of customary law.

Finally, the San Remo Manual provides that the passage rights applicable to archipelagic waters in peacetime shall continue to apply during an armed conflict. A neutral archipelagic state may condition, restrict or prohibit the entrance to or passage through its neutral waters by belligerent warships and auxiliary vessels on a non-discriminatory basis, “except for passage through archipelagic sea lanes” – whether formally designated or not.

Indonesia’s policy on the passage of AUKUS submarines through its archipelagic waters will have significant implications for its relationship with the countries involved and its commitment to uphold international law, especially if it attempts to prohibit or restrict the passage of foreign submarines in a manner inconsistent with its rights and obligations under UNCLOS. The legal principles and frameworks will undoubtedly play a crucial role in shaping the outcome.

Dita Liliansa is an Ocean Law & Policy Research Associate at the Centre for International Law (CIL), National University of Singapore (NUS). She earned her first law degree (LLB) from the University of Indonesia and Master of Laws (LLM) from the University of Washington as a Fulbright scholar. She has received recognition for her research work, including being awarded Second-Prize Winner of the 2021 Asian Society of International Law Junior Scholar Award. Apart from research, she is active in teaching university students and training government officials as well as participates in ASEAN and IMO meetings as an observer.

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The opinions expressed herein are the author's and not necessarily those of The Maritime Executive.