Straits, Submarines and Law of the Sea

During peacetime and training missions international law and international relations impact submarine movements in straits and narrows even if secrecy is assumed.

Impacting Russia’s invasion of Ukraine under the 1936 Montreux Convention, Turkey has the responsibility to monitor, regulate, and police the Turkish Straits, which consist of: the Bosphorus, Sea of Marmara and the Dardanelles. https://en.wikipedia.org/wiki/Montreux_Convention_Regarding_the_Regime_of_the_Straits

The Strait of Hormuz is also very topical given attacks against Iran and scope that these may soon prevent tankers from transiting this Strait https://www.tandfonline.com/doi/full/10.1080/00908320.2022.2096158#d1e158 .

On 2/07/2026 5:02 PM Shawn C Co-author of this Submarine and Nuclear Matters blog, made the very interesting points :  

“…I have stated before that the Straits of Malacca are an international passageway and governed under [the United Nations Convention on the Law of the Sea (UNCLOS)] https://www.un.org/depts/los/convention_agreements/texts/unclos/part3.htm )

Only the three littoral states, Indonesia, Malaysia and Singapore can jointly patrol the Straits (the Thais sometimes send a warship for joint patrols), so any country sending warships to unilaterally patrol the Malacca Straits, which lies in Malaysian and Indonesian territorial waters, would be ‘frowned upon’.

No nation can stop a ship who is exercising the right of innocent passage - this is why we can see Russian shadow fleet tankers sailing past Singapore. ( https://www.channelnewsasia.com/singapore/shadow-fleet-vessels-zombie-ships-sanctioned-cargo-oil-russia-iran-singapore-straits-5563491 )

If these ships were to pull out of the international lanes for whatever reason and enter Singapore’s territorial waters, they would immediately be stopped by Singapore’s Police Coast Guard.”

Pete Comment

Other UNCLOS aspects relate specifically to submarines.

Under UNCLOS (Article 20) the right of innocent passage for submarines is strictly regulated due to the potential threat they pose to coastal state security. To exercise innocent passage through a foreign territorial sea, submarines must navigate on the surface and show their flag.

Submerged passage without authorization constitutes a violation of the coastal state's sovereignty. For passage to be considered "innocent," it must not threaten the coastal state's peace, good order, or security, excluding activities like espionage or pollution.

Coastal states can impose restrictions, such as requiring submarines to use specific sea lanes, and can temporarily suspend innocent passage for security reasons.

This differs from "transit passage" through international straits, where submarines are permitted to remain submerged. Failure to comply with these rules can result in the coastal state ordering the submarine to leave its waters. Essentially, a submarine's right to innocent passage within 12 nautical miles of a foreign coast is limited to surfaced navigation.

Main Source: Kazuhiro Nakatani's, Submarines at Oxford Public International Law. last updated July 2008 at https://opil.ouplaw.com/display/10.1093/law:epil/9780199231690/law-9780199231690-e1839 A very comprehensive paper on the subject published under the auspices of the Max Planck Institute for Comparative Public Law and International Law under the direction of Professor Anne Peters (2021–) and Professor Rüdiger Wolfrum (2004–2020).