Arihant, Arighaat, Aridhaman: Inside India’s growing nuclear submarine triad against China, Pakistan

NEW DELHI: India's underwater deterrence is set to enter a decisive new phase with the induction of INS Aridhaman, the third Arihant-class nuclear-powered ballistic missile submarine, by May 2026.

Once INS Aridhaman joins INS Arihant and INS Arighat, India will operate three indigenously built SSBNs under the Strategic Forces Command.At a time when China is expanding its nuclear and conventional submarine footprint across the Indo-Pacific and Pakistan is inducting advanced Chinese-origin boats with air-independent propulsion, New Delhi’s strategic planners are steadily reinforcing the most secure and resilient leg of the nuclear triad — the sea.

Larger, quieter and armed with longer-range K-4 submarine-launched ballistic missiles, Aridhaman strengthens India’s second-strike capability and moves it closer to continuous at-sea deterrence.With Aridhaman joining INS Arihant and INS Arighaat, India now operates three indigenously built SSBNs under the Strategic Forces Command. This marks not just an incremental addition to naval inventory but a structural shift in India’s strategic posture.

As Beijing fields one of the world's largest submarine fleets and Islamabad bolsters its underwater arsenal, India's expanding SSBN force ensures credible minimum deterrence along with a devastating second-strike capability —stealthy, nuke-proof, and unstoppable — from the deepest depths of the Indian Ocean.

INS Arihant: The pioneer of India’s sea-based deterrence

Commissioned in August 2016, INS Arihant was the culmination of decades of classified work under the Advanced Technology Vessel programme.

Built at the Shipbuilding Centre in Visakhapatnam, Arihant displaced around 6,000 tonnes and was powered by an 83 MW Compact Light Water Reactor developed with significant indigenous input.Measuring roughly 111.6 metres in length, Arihant introduced India to the elite group of nations operating nuclear-powered ballistic missile submarines. Its propulsion allows virtually unlimited range, with endurance limited primarily by crew supplies.

Capable of speeds of around 24 knots submerged, it is designed for extended stealth patrols in the Indian Ocean Region.In terms of armament, Arihant carries four vertical launch system tubes. These can be configured to deploy up to 12 K-15 Sagarika submarine-launched ballistic missiles with a range of approximately 750 km, or four K-4 missiles with a reach of around 3,500 km. It also features six 533 mm torpedo tubes for defensive and conventional strike roles.The most important milestone came in 2018, when Arihant completed its first deterrence patrol. That patrol marked the operationalisation of India’s sea-based nuclear deterrent, completing the triad alongside land-based missiles and air-delivered systems. For Indian planners, Arihant represented assured retaliation — the guarantee that even in the worst-case scenario, India would retain a secure response capability beneath the sea.

INS Arighaat: Strengthening and sustaining deterrence

Commissioned on 29 August 2024, INS Arighaat built upon the foundation laid by Arihant. While similar in baseline displacement at around 6,000 tonnes, Arighaat is considered a refined and improved iteration of the class.Constructed at the same Visakhapatnam facility, Arighaat underwent extended harbour and sea trials before induction. Its nuclear propulsion system remains based on the pressurised light water reactor design, enabling prolonged submerged operations with minimal acoustic signature.Arighaat retains four vertical launch tubes but is widely regarded as optimised for longer-range K-4 missile deployment. The K-4 significantly expands India’s maritime strike envelope, allowing strategic targets to be held at risk from deeper within the Indian Ocean, reinforcing India’s protected retaliatory capability.Like Arihant, Arighaat carries six torpedo tubes and incorporates indigenous sonar suites such as USHUS and Panchendriya for underwater detection and combat management.

Improvements in onboard systems, quieting measures and operational protocols are believed to make it more capable during deterrence patrols.The induction of Arighaat was strategically important. A single SSBN cannot guarantee continuous deployment due to maintenance cycles and crew rest requirements. With two boats available, India moved closer to rotational deterrence patrols, ensuring greater availability of a secure and enduring second-strike platform.

INS Aridhaman: The 7,000-tonne evolution

INS Aridhaman represents the most advanced evolution of the Arihant-class to date. Weighing approximately 7,000 tonnes, it is significantly larger than its predecessors, allowing expanded missile capacity and system enhancements.One of its most consequential upgrades is the increase in vertical launch system tubes from four to eight. This expanded configuration enables Aridhaman to carry up to 24 K-15 missiles or eight K-4 intermediate-range ballistic missiles.

Reports also suggest potential accommodation for future K-5 missiles with ranges extending to around 6,000 km.Aridhaman is powered by an upgraded 83 MW Compact Light Water Reactor designed for reduced acoustic signature. A seven-blade propeller, advanced sound-dampening measures and extensive use of anechoic tiles enhance stealth characteristics. Submerged speeds are estimated at around 24 knots, with surface speeds between 12 and 15 knots.The increase in displacement provides greater internal volume for improved command-and-control systems, crew habitability during long patrols and advanced combat systems integration. Sonar systems, including USHUS and Panchendriya, enhance underwater situational awareness, while improved quieting measures strengthen its stealth advantage against adversary anti-submarine warfare platforms.Strategically, Aridhaman is pivotal because it accelerates India’s transition toward Continuous At-Sea Deterrence.

With three SSBNs, the navy can maintain at least one submarine on patrol at any given time, while others undergo maintenance or training cycles. This layered deployment model is central to India’s assured retaliatory posture.

The broader Indian Navy nuclear framework

India’s SSBN fleet operates under the Strategic Forces Command, which oversees nuclear assets. The sea-based leg is considered the most important component of the nuclear triad, as submarines operating silently beneath the ocean are far more difficult to detect and neutralise compared to fixed land-based systems.The submarines are expected to operate from Project Varsha, a high-security naval base near Visakhapatnam featuring underground pens designed to protect nuclear assets. The location provides strategic access to the Bay of Bengal and the wider Indian Ocean.India’s nuclear submarine ambitions extend beyond ballistic missile platforms. The navy is also set to induct Chakra III, a Russian Akula-class nuclear-powered attack submarine expected by 2027–28.

Unlike SSBNs, attack submarines focus on anti-ship, anti-submarine and escort missions, complementing strategic deterrence assets.

Conventional submarine modernisation: Project-75I

Parallel to the SSBN expansion, India is pushing forward with Project-75I, a programme to build six next-generation diesel-electric submarines equipped with air-independent propulsion. These boats are intended to replace ageing conventional platforms and enhance sea denial capability.The project, valued at approximately $8 billion, is designed to boost indigenous manufacturing under the Strategic Partnership Model. The selected German Type-214 Next Generation submarine features fuel-cell-based air-independent propulsion, allowing extended submerged endurance without snorkelling.

Air-independent propulsion provides critical tactical advantages in contested waters, reducing detection risk and enabling covert surveillance and strike roles.

Under the current plan, the submarines will be constructed at Mazagon Dock Shipbuilders Limited with technology transfer arrangements.Project-75I complements the SSBN fleet by strengthening conventional underwater capabilities, ensuring that India’s submarine arm can perform both strategic and tactical missions across the Indo-Pacific.

Towards continuous at-sea deterrence

Continuous At-Sea Deterrence requires more than one submarine.

Maintenance, refuelling, crew training and refits create availability gaps. Three operational SSBNs allow staggered deployments, ensuring that at least one remains on patrol.Aridhaman’s expanded missile payload also increases strike flexibility. The ability to deploy longer-range K-4 missiles from safer patrol areas enhances operational depth and strategic reach. As missile ranges increase in future variants, patrol patterns may evolve further into secure ocean bastions.India’s pursuit of second-strike capability reflects a doctrine rooted in credible minimum deterrence. The objective is not numerical parity but guaranteed retaliation capability.

Comparison with China and Pakistan’s submarine fleets

India’s expanding SSBN fleet must be viewed against the backdrop of rapid underwater modernisation by both China and Pakistan. While New Delhi has prioritised a credible sea-based nuclear deterrent anchored in three Arihant-class boats, Beijing and Islamabad are pursuing parallel — though structurally different — submarine strategies.China operates one of the world’s largest submarine forces under the People’s Liberation Army Navy. Open-source defence assessments estimate that China fields more than 50 diesel-electric submarines and around 10 nuclear-powered submarines, including both attack submarines (SSNs) and ballistic missile submarines (SSBNs). Its Jin-class SSBNs are armed with JL-series submarine-launched ballistic missiles, giving Beijing an established sea-based nuclear capability.

Chinese nuclear submarines have increasingly deployed into the Indian Ocean, occasionally docking at regional ports, a development closely monitored by Indian naval planners.

Pakistan, though operating a much smaller fleet, is upgrading steadily with Chinese assistance. The Pakistan Navy currently relies on ageing Agosta-class submarines but is in the process of inducting eight Yuan-class diesel-electric submarines from China, many equipped with air-independent propulsion.

While Pakistan does not yet operate nuclear-powered submarines, its conventional fleet — particularly with AIP — enhances underwater endurance and sea-denial capability in the Arabian Sea.

The strategic distinction lies in composition and doctrine. China maintains a full-spectrum submarine fleet spanning nuclear attack submarines, ballistic missile submarines and advanced conventional boats. Pakistan focuses on sea denial and coastal defence, aiming to counterbalance India’s conventional naval superiority.

India’s approach sits between the two: a modest but growing SSBN fleet for strategic deterrence, complemented by conventional submarines under Project-75 and Project-75I, and future nuclear-powered attack submarines.Numerically, India trails China in total submarine count. However, its objective is not parity but credible deterrence within its maritime theatre. Against Pakistan, India retains an edge in nuclear-powered capability, as Islamabad lacks SSBNs or SSNs.

The induction of INS Aridhaman and the planned arrival of Chakra III strengthen that qualitative advantage.In effect, India’s submarine modernisation is less about fleet size and more about stealth, endurance and strategic depth. As China expands its blue-water reach and Pakistan upgrades its conventional arm, India’s triad-backed SSBN force is intended to ensure that deterrence remains intact beneath the surface of the Indian Ocean.