Submarines May Transit Submerged and Aircraft Fly Freely: How UNCLOS Article 38 Strips Coastal Vetoes Over International Straits

On November 16, 1994, the entry into force of the United Nations Convention on the Law of the Sea fundamentally altered the sovereign geometry of the world's oceans. By codifying the right of transit passage, the treaty stripped coastal nations of their ability to veto foreign military movements through international straits.[1]

The legal shift resolved a crisis triggered by the global expansion of territorial waters. As coastal states unilaterally extended their sovereign boundaries from three to 12 nautical miles, approximately 116 international straits were suddenly enclosed by domestic jurisdictions.[3]

Without a new legal framework, global navies and commercial fleets would have been subject to the whims of coastal governments. If standard territorial sea rules applied, bordering nations could dictate exactly who passed through, effectively paralyzing maritime mobility.

The 1982 UNCLOS text engineered a specific legal carve-out to prevent this. Article 38 established the revolutionary right of transit passage, ensuring that international straits remained open to the world despite the expansion of territorial waters.[1]

Under this regime, the waters and airspace of international straits are treated as a distinct jurisdictional zone. The law explicitly strips bordering nations of the authority to suspend, hamper, or impede the continuous and expeditious transit of foreign vessels and aircraft.[1]

The Submerged Transit Exception

In standard territorial waters, UNCLOS Article 20 dictates a strict and uncompromising rule of "innocent passage" for submarines. They are legally required to navigate on the surface and prominently display their national flag, ensuring coastal states can monitor military assets near their shores.[1][3]

Transit passage under Article 38 completely dismantles this surface requirement. Because the law permits vessels to transit in their "normal modes of operation," military submarines are legally authorized to remain submerged while passing through international straits.[1]

This distinction serves as a cornerstone of modern naval strategy and nuclear deterrence. The U.S. Navy’s Commander's Handbook on the Law of Naval Operations explicitly affirms this doctrine, stating that "submarines may transit while submerged and that surface warships may carry out those activities normally undertaken during passage."[2]

For major maritime powers, the ability to move ballistic missile submarines and attack fleets through chokepoints undetected is a non-negotiable security imperative. The transit passage regime legally protects this stealth capability against any coastal state interference or domestic legislation.[2]

The "normal mode" provision extends beyond submarines to surface fleets. Aircraft carriers transiting a strait are legally permitted to launch and recover helicopters and fixed-wing aircraft, and naval task forces can maintain defensive formation steaming, actions that would be strictly prohibited under innocent passage.

Unrestricted Airspace and Overflight

The jurisdictional void created by Article 38 extends vertically into the sky, creating a unique aviation environment. While coastal states possess absolute and exclusive sovereignty over the airspace above their standard territorial waters, international straits are exempt from this control.[1]

Foreign aircraft, including military bombers, fighter jets, and surveillance planes, enjoy an unrestricted right of overflight through these corridors. They do not need to file flight plans, request diplomatic clearance, or identify themselves to the nations bordering the strait.[3]

"The silence of the UN Convention on the Law of the Sea on this point gives foreign civil and military aircraft the right to exercise freedom of overflight anywhere from shore to shore in the airspace of the strait," notes Oxford Public International Law, highlighting the expansive nature of the aviation rights.

This principle was starkly demonstrated in April 1986, when U.S. military aircraft flew through the airspace over the Strait of Gibraltar to conduct bombing operations against targets in Libya. Neither Spain nor Morocco could legally protest the overflight, as the airspace was governed by transit passage.

The lack of coastal veto over airspace ensures that military alliances can rapidly deploy air assets across the globe. Without Article 38, a single coastal state could effectively block an entire air corridor, forcing aircraft to take massive detours over the high seas.

The Limits of Coastal Authority

While Article 38 grants sweeping freedoms to transiting forces, UNCLOS imposes specific duties to balance the security and environmental concerns of coastal states. Article 39 requires that ships and aircraft proceed without delay and refrain from any threat or use of force.[1]

Transiting vessels are strictly prohibited from conducting marine scientific research, surveying activities, or offensive military exercises while in the strait. The passage must remain solely for the purpose of moving from one part of the high seas or exclusive economic zone to another.[1]

Coastal states retain the authority to enforce internationally approved safety and environmental regulations. Under Article 41, they can designate sea lanes and traffic separation schemes, provided these are adopted by the International Maritime Organization rather than imposed unilaterally.[1]

However, coastal states cannot use these regulatory powers as a pretext to block access or discriminate against specific nations. Article 44 of UNCLOS explicitly forbids bordering nations from suspending transit passage for any reason, including live-fire military exercises or heightened geopolitical tensions.[1]

This absolute prohibition on suspension is the critical mechanism that separates transit passage from innocent passage. Under innocent passage, a coastal state can temporarily halt traffic if it deems the passage a threat to its security; under transit passage, the corridor must remain open permanently.[1]

Defensive Maneuvers and Force Majeure

The prohibition against the threat or use of force in Article 39 is frequently tested in contested waterways. Coastal states often deploy fast-attack craft or drones to shadow transiting warships, attempting to assert dominance without crossing the threshold of an armed attack.

In response, transiting naval forces rely on the legal exemptions built into the transit passage framework. UNCLOS explicitly permits ships and aircraft to deviate from their normal modes of continuous and expeditious transit if they are rendered necessary by force majeure or distress.[1]

"UNCLOS allows ships and aircraft conducting transit passage to deviate from their 'normal mode of activity' if they encounter force majeure or distress," notes the Washington Institute for Near East Policy, emphasizing that defensive maneuvers against threatening speedboats remain legally protected.

This ensures that a warship is not legally forced to absorb an attack or endure dangerous harassment simply to maintain its transit status. Commanders retain the inherent right of self-defense, and taking evasive action does not invalidate their right to traverse the strait.[2]

Archipelagic Sea Lanes and State Practice

The principles of transit passage were also adapted to address the unique geography of island nations. UNCLOS Article 53 established "archipelagic sea lanes passage," applying similar unhindered transit rights to the internal waterways of nations like Indonesia and the Philippines.[1]

Like transit passage, archipelagic sea lanes passage allows submarines to remain submerged and aircraft to conduct unannounced overflights along designated routes. This ensures that vast archipelagos do not become impenetrable barriers to global maritime and aviation traffic.[1][2]

Despite the clarity of the UNCLOS text, the application of transit passage remains a persistent flashpoint in global geopolitics. Nations bordering strategic straits frequently attempt to assert greater domestic control over the military vessels passing their shores.

Iran, for example, has historically argued that transit passage rights in the Strait of Hormuz apply only to the 168 nations that have formally ratified UNCLOS. This stance is aimed directly at the United States, which recognizes the rules as customary international law but remains a non-party to the treaty.

The Washington Institute for Near East Policy highlights that Iranian Islamic Revolutionary Guard Corps vessels frequently attempt to monitor or challenge foreign warships, framing their actions as a defense of sovereignty. Yet, under the transit passage framework, these warships are operating entirely within their legal rights.

The durability of Article 38 relies entirely on the willingness of maritime powers to continuously exercise their rights. By routinely sending submerged submarines and military aircraft through these corridors, global navies reinforce the legal norm that international straits belong to the world.[2]