Since Frank Hoffman coined the term “hybrid warfare” in 2007,¹ numerous articles and books have been written on this theme from the perspective of military studies and international relations.² Yet the existing legal literature has not so far focused on the challenges that hybrid warfare poses for the order of the oceans. One of the main current research gaps lies in the lack of clear understanding on how the law of the sea operates in hybrid warfare.³

The principal question is how can the law of the sea contribute to ensuring the rule of law in major shipping routes impacted by hybrid warfare? Another fundamental research problem lies in the ambiguities of how hybrid naval warfare or conflict differs – if at all – from traditional concepts of naval warfare or law enforcement operations. The implications of hybrid warfare for ocean governance deserves to be examined, as well as the usefulness of the concept of hybrid warfare for assessing the (il)legality of an aggressor’s actions in the maritime domain.

Hybrid Warfare as a Challenge to the Rights of Navigation

The means of hybrid naval warfare include the use of firearms and explosives, arrests of ships, cyberattacks, threats of force, economic coercion, and grey maritime networks, to name a few.⁴ Its scope may also include industrial projects that cause ecological destruction and pose security threats in the maritime domain. Notable examples include the construction of the Kerch Strait Bridge in the Black Sea, subsurface Nord Stream pipelines in the Baltic Sea, and artificial islands in the South China Sea that are allegedly detrimental to the marine environment and are protested against by the coastal states that are impacted by these construction activities.

Coastal states may perceive such industrial projects in their adjacent waters as a threat to their national security. For example, Finland’s defense minister has referred to concerns that are largely shared with the neighboring Baltic States that Russia could use its armed forces during a conflict situation to control the Nord Stream pipelines that cross Finnish, Swedish, and Danish maritime zones.⁵ Ukraine has similar concerns in respect of the Kerch Strait Bridge and much of the international community in relation to the artificial islands in the South China Sea. These projects have also created new challenges for the rights of navigation in the relevant maritime areas and thus for the stability of the law of the sea.

In 2018, the volume of seaborne trade reached over 11 billion tons which accounts for approximately 90 percent of global trade.⁶ Hybrid warfare is a hindrance to navigation in important maritime routes and has a negative impact on the stability of global commerce. In particular, such challenges to the rights of navigation go against the strategic maritime security interests of the European Union (EU) and its member states, which are “[t]he preservation of freedom of navigation, the protection of the global EU supply chain and of maritime trade, the right of innocent and transit passage of ships and the security of their crew and passengers.”⁷ The United States shares these interests and, in pursuance of these aims, operates the freedom of navigation program for the protection of navigation rights. In the example of freedom of navigation operations carried out in the South China Sea this has primarily caused tensions with China. Similarly, United States warships have repeatedly encountered dangerous approaches from the Iranian navy vessels in the Persian Gulf and Russian warships and aircraft in the Baltic Sea.

Russia, China, and Iran are three states which are primarily associated with the adoption of techniques of hybrid conflict.⁸ They are also important law of the sea actors, whose maritime areas include or are proximate to strategic waterways.

It is estimated that the rate of crossings in the South China Sea amounts to more than half of the world’s merchant fleet capacity,⁹ and the Baltic Sea is an area where approximately 15 percent of global cargo is trafficked.¹⁰ The Baltic Sea, the South China Sea, the Strait of Hormuz, and the Black Sea are also strategically important routes for oil and gas shipments.¹¹ The Baltic Sea, which is already heavily used for the export of Russian oil, is also destined to become the biggest route for the transportation of Russian natural gas to Europe, overshadowing the main alternative transit route in Ukraine.¹² The Black Sea, which holds itself as much natural gas reserves as the North Sea, is used by Russia as one of its main routes for oil shipments and is also destined to become crossed by many subsurface pipelines.¹³ Furthermore, the Strait of Hormuz is one of the main global chokepoints for the transportation of oil. Approximately a fifth of global oil exports are shipped via the Strait of Hormuz.¹⁴

The strategic importance of these maritime regions shows how significant it is to uphold the rule of law and safeguard the passage rights therein. However, these maritime regions are also areas where the stability of navigation is currently under pressure due to the coastal states’ shifting security considerations and methods of hybrid conflict. Foreign ships that were navigating through important chokepoints of maritime commerce have recently repeatedly been subjected to the use of force or coercion by some coastal states. Notable examples include the Kerch Strait incident of November 25, 2018, and the Strait of Hormuz incidents in the summer of 2019. 

Regional Examples of Grey Zones in Maritime Hybrid Conflict

The grey zone in hybrid warfare can be understood as a space short of clear-cut military action wherein the aggressor creates enough ambiguity to reach its strategic objectives without engaging in an open offensive.¹⁵ In the Kerch Strait incident of November 2018, Russia arguably made use of legal uncertainty by operating in a grey zone for complicating decision-making for other states. It seized three Ukrainian naval ships, including two warships, and arrested their crew as they were entering the Kerch Strait under freedom of navigation. In the context of the annexation of Crimea and armed conflict in eastern Ukraine, this incident has raised the question of whether Russia’s actions in the Kerch Strait should be considered as being undertaken in the legal framework of international humanitarian law.¹⁶ In other words, it is not entirely clear to what extent the law of the sea applies in hybrid warfare or conflict. This is intertwined with the question of whether the law of naval warfare or the legal framework on law enforcement should be applied in so-called grey areas to assess the legality of the coastal State’s use of force or direct coercion on the sea.

In the Kerch Strait incident Russia acted openly by using its Coast Guard vessels. By contrast, in the attacks against two oil tankers at the approaches to the Strait of Hormuz in the summer of 2019, the aggressor used a covert operation. In the context of the South China Sea, China’s activities in a grey zone allegedly include both elements, such as the use of law enforcement and a maritime militia in an escalatory manner to deter the use of natural resources by other states.¹⁷

As widely acknowledged, the passage rights of foreign ships and aircraft are at the center of tensions between China and the user states of navigation routes in the South China Sea.¹⁸ By contrast, Russia’s practice in relation to the passage rights of ships and aircraft in, above and near its maritime areas in the Baltic Sea (such as the eastern part of the Gulf of Finland and adjacent to the Kaliningrad enclave) has largely remained unnoticed in legal research. The repeated unsafe actions of Russian fighter jets against U.S. warships that have entered the Baltic Sea, the incursions of suspected Russian submarines into the territorial seas of Sweden and Finland, as well as the multiple violations of Estonia’s airspace by Russia’s aircraft are all instances that merit further attention in the context of hybrid conflict in the Baltic Sea region.¹⁹

In other occasions, tensions between the coastal states of the Gulf of Finland have had a direct adverse impact on the passage rights of ships. For example, in the aftermath of the 2007 riots which were sparked in the Russian-speaking minority in Tallinn due to the relocation of the Soviet Bronze Soldier monument, Russia declined to give its authorization for crossing its territorial sea under the right of innocent passage to the commercial ship Vironia. She transported goods and passengers in the eastern Gulf of Finland between the Estonian Sillamäe Port and the Finnish Kotka Port. Russia effectively caused the closure of the ferry line.

In practice, the Nordic States acknowledge the threats of hybrid warfare and actively prepare to counter such challenges in the northern Baltic region.²⁰ For example, the first large-scale training exercise of the United Kingdom-led Joint Expeditionary Force was aimed at countering threats emanating from a hypothetical hybrid warfare in Estonia, including its maritime domain.²¹ Likewise, the Finnish defence minister has cautioned against the possibility that the demilitarized Åland Islands are turned into a theater of war by so-called little green men in case a foreign state is willing to breach the rules of international law.²²