Straits, Transit Passage, and Conflict: UNCLOS and Laws of Armed Conflict at Sea

by Captain Sarabjeet S Parmar (Retd)

Introduction

The world’s critical maritime chokepoints, the narrow straits through which global trade and other shipping transits, have always carried enormous strategic weight. In peacetime, the rules governing straits are codified in the United Nations Convention on the Law of the Sea 1982 (UNCLOS 1982). It enshrines the right of ‘transit passage’ through international straits, and states that all ships and aircraft, including warships, may pass through straits used for international navigation ‘continuously and expeditiously’ without being hampered, and does not permit suspension of the passage. It also applies to passages through straits that run through the territorial seas of adjoining coastal nations, where transit passage supersedes ‘innocent passage’. However, the situation changes when conflict erupts. The legal architecture of transit passage, designed for the peaceful use of the seas, comes under strain, and the consequences of nations’ actions in conflict ripple far beyond the main theatre of conflict.

The Strait of Hormuz: Flashpoint for Legal and Strategic Crisis

The Persian Gulf is geographically a cul-de-sac, with the Strait of Hormuz as the sole point of entry and exit. For energy-hungry global economies, this Strait has been a source of concern and anxiety fuelled by decades of instability, driven by sabre-rattling and military rhetoric. The ongoing US-Israel-Iran conflict was inevitable, and nations should not be surprised by the ripple effects, which are slowly building into a Tsunami. The conflict and associated threats, risks, and challenges need to be analysed for their implications for the other straits that ring the Indian Ocean Region (IOR). A geographical comparison of the straits in the IOR is presented in the table.

Comparison of IOR Straits (Km – Kilometres, m – metres)

Strait	Length	Width	Depth	Adjoining Coastal Nations
Hormuz	167 km	Average: 39 – 97 km Narrowest: 33 – 39 km	60 – 100 m Average: 70 m	Iran, Oman, UAE
Bab el-Mandeb	150 km	Average: 26 – 32 km West Channel: 25 km East channel: 5 km	West channel: 310 m East channel: 29 m with Sill at 160 m	Yemen, Djibouti, Eritrea
Malacca	800 – 900 km	Average: 65 – 250 km Narrowest: 2.8 km in Phillips Channel	Minimum 25 m to 200 m at the Northwest end	Malaysia, Indonesia, Singapore
Singapore	113 km	Average: 16 – 19 km Narrowest: 2.7 km	20 – 120 m	Malaysia, Indonesia, Singapore
Sunda	150 km	Average: 26 – 110 km Narrowest: 24 km	Minimum 20 m at the Northeast end, up to 1,080 m at the Southwest end	Indonesia
Lombok	60 km	Average: 18 – 40 km Narrowest: 18 km at the Southern end	Minimum 250 m, up to 1,200 m at the Northern end	Indonesia
Ombai	@ 200 km	Average: 27 – 35 km Narrowest: 27 km	Up to 3,250 m Near coast: 3,000 m	Indonesia, Timor-Leste
Wetar	@ 120 km	Minimum: 42.6 km	Deep water passage Minimum: 2,450 m (Sill depth)	Indonesia, Timor-Leste

Source: Compiled by Author from Various Sources

Ships navigating these straits transit through the maritime zones, essentially the Territorial Seas (TS) of the coastal nations adjoining the straits. Shipping enjoys the freedom of transit passage through straits and innocent passage through the TS of a coastal state. Articles 44 and 45 of UNCLOS clearly state that there will be no hampering or suspension of transit or innocent passage through straits used for international navigation. However, this may not be considered inviolable by both Iran and the US, as the US has neither signed nor ratified UNCLOS, and Iran has signed but not ratified it. From a legal standpoint, Iran, as a signatory to UNCLOS, is technically bound by the transit passage regime. By comparison, successive US administrations have treated the core navigation and overflight provisions of UNCLOS as reflective of customary international law and have committed to operating in accordance with those provisions.

UNCLOS and Laws of Armed Conflict at Sea

Over time, one aspect has become clear. Interpretations of UNCLOS that support national interests have dictated state behaviour, and the lack of enforcement mechanisms has weakened the convention. Iran’s recent legislation imposing transit fees on commercial vessels passing through the Strait of Hormuz is based on its non-ratification of UNCLOS. However, transit passage is also part of customary international law, derived from centuries of state practice and opinio juris, which binds all states regardless of treaty status. Any toll can be interpreted as ‘hampering’ passage. 

Currently, the situation in the Strait of Hormuz is marked by a clash between UNCLOS, which focuses on the peaceful uses of the oceans, and the Laws of Armed Conflict at Sea, which govern how nations conduct warfare in the maritime domain. The Laws of Armed Conflict at Sea distinguish between ships that may be targeted and those that may not. For example, enemy warships, military aircraft, and auxiliary vessels and aircraft may be targeted, while merchant vessels and civil aircraft are not to be targeted unless they satisfy military objective criteria. Similarly, certain enemy ships and aircraft, such as hospital ships and medical aircraft, cannot be targeted, and neutral shipping cannot be targeted. During a conflict, neutral shipping, including warships, aircraft, and auxiliaries, continues to enjoy the right of transit passage through international straits, even if the passage is through a belligerent’s maritime zone. However, timely notice of passage, as a precautionary measure, is advised. The US blockade of all maritime traffic entering or exiting Iranian ports and coastal areas met all criteria except one – it did not specify the period within which vessels of neutral States may leave the blockaded coastline. Actions taken by belligerents, such as hampering or stopping the transit passage of neutral shipping and firing on them, are serious and can be considered an act of war by the flag state. The positioning of warships by nations for escort duties increases the risk of a stand-off and drastically reduces the margin for error. 

Conclusion

The prevailing legal view is that transit passage should supersede the actions of belligerent nations in conflict. However, if the strait’s bordering state is itself a belligerent, the situation becomes more challenging. The belligerents may seek to interdict enemy vessels, lay minefields, or enforce a blockade, measures that in practice amount to a closure, whatever the legal justification offered. Therefore, the Strait of Hormuz crisis is not merely a regional problem. It is a stress test for international maritime law, one whose results will shape how states behave in every other strait during a crisis.

The views expressed here are the author’s personal views.