When the Iranian naval vessel IRIS Dena sank near Sri Lanka, questions quickly arose about India’s responsibility in what many are calling its maritime backyard. The vessel had recently participated in a naval exercise in Visakhapatnam before issuing a distress call that prompted search-and-rescue assistance from the Indian Navy.Incidents in the region are often interpreted through the assumption that the Indian Ocean forms India’s principal maritime sphere of influence, even as New Delhi frames its regional role as that of a “net security provider” through maritime surveillance, anti-piracy operations and regional security assistance.Under the United Nations Convention on the Law of the Sea (UNCLOS), coastal sovereignty extends only 12 nautical miles into the territorial sea, while the Exclusive Economic Zone (EEZ) reaches 200 nautical miles and grants economic rights over resources but not authority over foreign military operations. Much of the ocean beyond these zones, therefore, is governed by the principle of freedom of navigation.Yet the IRIS Dena incident raises a question: Who is responsible for security and crisis response in the Indian Ocean’s busiest sea lanes? This question is less one of jurisdiction and more related to the wider strategic structure of the Indian Ocean, where dense commercial shipping, critical energy flows and expanding naval deployments intersect across some of the world’s busiest sea lanes.The Indian Ocean as a strategic maritime arteryThe waters south of Sri Lanka where the IRIS Dena sank lie along one of the busiest maritime corridors of the world. Nearly 1,00,000 ships transit the Indian Ocean annually, carrying roughly 30% of global container traffic and about 42% of crude oil trade.These sea lanes carry more than one-third of the world’s bulk cargo and nearly two-thirds of global oil shipments linking West Asian energy supplies with the industrial economies of Asia, making it central to the smooth functioning of the global economy.Much of this energy traffic moves across the Indian Ocean toward the Strait of Malacca, the world’s largest oil transit checkpoint, which handles about 29% of global seaborne oil trade. The Strait of Hormuz alone accounts for roughly 34% of seaborne oil exports, making it a vital route and strategically sensitive.At the same time, global maritime trade itself continues to expand. UNCTAD estimates that shipping volumes grew 2.2% in 2024, while the average maritime transport distance increased from 4,831 miles in 2018 to 5,245 miles in 2024. In other words, trade routes have continued to reconfigure amid geopolitical disruptions.And where trade flows concentrate, naval presence inevitably follows. These same sea lanes attract the sustained presence of major naval powers. The United States (US) sustains a forward presence through its Fifth Fleet, recommissioned in 1995 for operations across the Persian Gulf, Arabian Sea and western Indian Ocean. It typically deploys 15 to 35 warships.Diego Garcia in the Indian Ocean supports this posture of the US, with 19 pre-positioning ships – cargo ships loaded with military equipment and supplies stationed near potential conflict zones – capable of sustaining about 16,500 troops for 30 days. China has similarly expanded its operational footprint across the Indian Ocean through a rising tempo of military exercises with regional partners. The number of Chinese exercises in the region rose from seven between 2020 and 2022 to fourteen in 2023, with 12 further drills conducted across the Arabian Sea, Gulf of Oman and the Mozambique Channel through 2024 and early 2025.Despite these deployments, the Indian Ocean remains structurally resistant to control – many navies operate there, but no country can control the entire ocean because it is too vast. Spanning more than 70 million square kilometres, it makes persistent surveillance across the basin extremely difficult for any single navy. Such an environment makes martime security contingent on the capacity of states to monitor activity rather than jurisdiction.India’s maritime exposure and expanding naval capabilityAround 95% of India’s trade by volume moves by sea, making maritime stability along Indian Ocean routes essential to its economic functioning. The scale of this maritime commerce is visible in port activity as well. During April-January 2025-26, Indian ports handled approximately 756 million metric tonnes (MMT) of cargo, up from 698 MMT during the same period in 2024-25.India’s maritime exposure is also geographic. The country possesses an 11,098-kilometre coastline and an EEZ of roughly 2.4 million square kilometres, placing it within one of the world’s most active maritime theatres.Since 2008, Indian naval deployments in the Gulf of Aden and the western Indian Ocean have facilitated the safe transit of 3,765 merchant vessels and protected more than 27,000 seafarers through anti-piracy operations. These structural realities explain the scale of India’s naval modernisation effort. Government data indicate that 51 major naval platforms are currently under construction in Indian shipyards, representing projects worth roughly Rs 90,000 crore.Since 2014, more than forty indigenous warships and submarines have entered service, with new platforms inducted roughly every forty days in recent years – approximately one new naval platform every six weeks, and expansion continues.Long term planningIndia operates around 150 warships and naval planners expect the fleet to expand towards 230 vessels by 2037, giving it a more sustained presence across the Indian Ocean and adjoining Indo-Pacific sea lanes.In this context, the IRIS Dena episode highlights the growing strategic imperatives of undersea warfare. The incident shows us why submarines and underwater military capabilities are becoming more important in naval strategy. Submarines remain the most difficult naval platforms to detect, enabling states to influence maritime corridors without without visibly deploying ships.Undersea capability forms a central element of this strategy. India operates around nineteen submarines, compared with more than sixty in China’s fleet, a strategic asymmetry in undersea competition in the Indo-Pacific that is crucial to address.Bridging this gap in capabilities is a central objective of programmes such as Project-75 and Project-75I. Under the latter, India plans to construct six next-generation conventional submarines with Germany’s Thyssenkrupp Marine Systems, in a deal estimated at roughly USD 8 billion and centered on air-independent propulsion technology that allows submarines to remain submerged for extended periods.These capabilities are complemented by investments in maritime domain awareness, including the GSAT-7R naval communication satellite, designed to connect ships, aircraft and maritime command centers across the Indian Ocean in real time.The Indian Ocean may bear India’s name, but it remains one of the world’s most contested maritime commons – which needs greater regional and sovereign attention. For New Delhi, the challenge is not to control this oceanic expanse but to build the surveillance capability, undersea ability and strategic partnerships required to secure its interests within it.Saksham Raj and Aditi Lazarus, research analysts with Centre for New Economics Studies, O.P Jindal Global University, contributed to this column.