Gajendra Singh Godara
Aug 24, 2025
15
mins read
Ballistic missile submarines (SSBNs) are nuclear-powered submarines capable of launching submarine-launched ballistic missiles (SLBMs) armed with nuclear warheads. They are a key element of a country’s nuclear triad (land, air, sea), providing a hidden and mobile second-strike capability. Such submarines can launch missiles from thousands of kilometers away while remaining submerged and undetected.
India’s SSBN fleet so far includes INS Arihant (S2) and INS Arighaat (S3). INS Aridhaman (SSBN-82) is the third Arihant-class SSBN, designated S4, being built under India’s Advanced Technology Vessel (ATV) program. It is expected to join the Navy around 2025, completing the sea leg of India’s strategic deterrent.
Purpose: SSBNs carry nuclear warheads on SLBMs to deter nuclear attacks by guaranteeing retaliation. In a first-strike scenario by an adversary, hidden SSBNs ensure India can still retaliate (second-strike), thereby stabilizing deterrence.
India’s Triad: India’s nuclear doctrine aims for a credible minimum deterrent. With land (Agni missiles) and air (fighter-bombers) components established, SSBNs like Aridhaman provide the sea-based leg. India is one of the few countries (with US, Russia, China) to field a full triad.
UPSC Relevance: The development of INS Aridhaman ties into UPSC topics like India’s nuclear doctrine, defence indigenization, and maritime strategy. For related UPSC content, see PadhAI’s articles on ballistic missile technology and deterrence (e.g. Pralay Missile , Operation Rising Lion Explained , Drone Warfare, UPSC CDS 2025 Exam).
India is poised to significantly enhance its strategic defence capabilities with the upcoming induction of its third nuclear-powered Ballistic Missile Submarine (SSBN), INS Aridhaman.
INS Aridhaman was launched in 2021, currently in trials, and expected to be commissioned by 2025.
Advanced Design: Aridhaman is slightly larger than its predecessors (INS Arihant and INS Arighaat) and carries more long-range SLBMs. It can mount K-4 missiles (~3,000+ km range) for stronger strike capability.
Strategic Deterrence: SSBNs like Aridhaman are the stealthiest leg of the nuclear submarines triad, ensuring a survivable second-strike capability. Media note that SSBN patrols (months submerged) are “the most secure, survivable and stealthy platforms for second-strike” under India’s no-first-use doctrine.
Table of content
INS Aridhaman is an upgraded Arihant-class Submarine SSBN (S4 series) with enhanced strike capacity. Key design features include:
Advanced Reactor: Powered by an indigenously designed 83 MW pressurized light-water reactor (CLWR) developed by BARC. This reactor provides greater power with a reduced noise signature, allowing submerged speeds up to 24 knots. Endurance is effectively unlimited (limited only by food and crew supplies).
Larger Hull: Displacement is about 7,000 tonnes – roughly 1,000 tonnes heavier than the earlier SSBNs. The hull is stretched to ~130 m length, providing room for more missile tubes and equipment. (By comparison, INS Arihant displaces ~6,000 tonnes.)
Missile Payload: INS Aridhaman is equipped with eight vertical launch tubes—double the four on INS Arihant and Arighaat. Each tube can host one medium-range K-4 SLBM (3,500 km range) or three short-range K-15 “Sagarika” SLBMs (750 km range), allowing a total load of either eight K-4 missiles or 24 K-15 missiles. Future integration of K-5 SLBMs (6,000 km range) is planned, further enhancing Aridhaman’s salvo capacity.
Sensors and Systems: Equipped with advanced USHUS and Panchendriya sonar suites and twin flank-array hydrophones, Aridhaman can detect threats and targets undersea. It also has indigenous fire-control and navigation systems. The design is reportedly ~70% indigenous, with major contributions from DRDO, L&T, Tata and other Indian industries. Countermeasures include Rafael-built anti-torpedo decoys and an underwater communication system.
Stealth and Endurance: The upgraded reactor and improved silencing make INS Aridhaman quieter than its predecessors. Like all SSBNs, it can remain submerged for months, making it a survivable deterrent asset.
The Arihant-class SSBNs (INS Arihant S2, INS Arighaat S3, and INS Aridhaman S4) share common features with some advances:
Nuclear Propulsion: All submarines have onboard nuclear reactors (~83 MW) for extended range and endurance, unlike diesel-electric subs. With nuclear power, Arihant-class boats have unlimited range, constrained only by crew and food, enabling patrols across the Indo-Pacific.
Armament: INS Arihant and Arighaat each have 4 SLBM tubes (capacity for 12 K-15 or 4 K-4 missiles). Aridhaman doubles this to 8 tubes. The switch from K-15 (750 km) on Arihant to K-4 (3,500 km) on newer subs greatly extends strike reach. (The first two boats are now being fitted to launch K-4 as well.)
Size and Displacement: Arihant-class vessels displace 6,000–7,000+ tonnes. INS Aridhaman (S4) is ~7,000t, larger than the 6,000t Arihant/Arighaat. Increased size allows more missiles, torpedo tubes, and accommodation for larger crews (~95 personnel).
Sensors/Comms: Equipped with advanced sonar (bow and flank arrays), inertial navigation, periscopes, and secure satcom. These enable long-duration patrols while staying in touch with Naval HQ.
Strategic Improvement: Compared to India’s leased Akula-class SSN (INS Chakra), which is an attack (hunter-killer) sub, Arihant-class has SLBMs for nuclear strike. Compared to conventional diesel subs, it has far greater stealth and operational range. The Arihant program thus “significantly strengthened India’s nuclear deterrent”.
Unlike attack submarines (SSNs or diesel-electric boats), INS Aridhaman is designed for strategic nuclear deterrence, not tactical combat. The table below highlights key differences:
Feature | INS Aridhaman (SSBN) | Nuclear Submarine (e.g. INS Chakra) |
Mission Role | Nuclear-armed deterrence (sea-based leg) | Conventional warfare (anti-ship, anti-sub, reconnaissance) |
Propulsion | Nuclear (83 MW CLWR reactor) – unlimited range | Nuclear (190 MW Akula reactor) – unlimited range |
Armament | 8 SLBM launch tubes (K-4, K-15 nuclear missiles) + torpedoes | Torpedoes, cruise missiles (e.g. BrahMos), naval mines (no SLBMs) |
Warheads | Nuclear warheads (via SLBMs) | Conventional munitions |
Stealth/Endurance | Designed for maximum stealth/deep patrols; months submerged | Also stealthy, but mission profile focuses on shorter-range patrols |
Endurance | Months (nuclear reactor) | Months (nuclear reactor) |
Size/Displacement | ~7,000 tonnes | INS Chakra (Akula-class) ~8,000 tonnes (large) |
Crew | ~95 officers & sailors | ~70–90 (varies by class) |
Strategic Value | Second-strike nuclear deterrent (credible no-first-use) | Enhances naval power projection and anti-sub capabilities |
The INS Aridhaman will play a crucial continuing role in India’s nuclear strategy and maritime security:
Nuclear Submarines Triad: Once commissioned, Aridhaman (S4) will ensure India has multiple SSBNs at sea, meeting the need for credible minimum deterrence. A fourth SSBN (S5) is under construction, and India plans even more advanced SSBNs with larger reactors (S4* with 6,000t and next-gen 13,500t with 190 MW reactors).
Joint Exercises & Patrols: The Navy will conduct deterrence patrols (continuous secret deployments) for Arihant-class boats. Regular training ensures crew readiness and system validation. India may also participate in multinational naval exercises, showcasing its sea-based deterrence.
Infrastructure Development: Project Varsha – a new high-security nuclear submarine base at Rambilli (Andhra Pradesh) – is nearing completion. Slated to be operational by 2026, Varsha will house SSBNs like Aridhaman in underground pens, allowing them to quietly slip into the Bay of Bengal for patrols.
Next-Gen Submarines: Beyond Arihant-class, India is conceptualizing SSBN V (larger hull, more missiles) and building six nuclear-powered attack submarines (SSNs) for conventional roles. The Cabinet has approved two new SSNs (6 planned) for ~$40,000 Cr.
The induction of INS Aridhaman thus represents a significant step in India’s naval modernization and nuclear deterrent strategy. It will help ensure India’s second-strike capability is robust and cre
Q. What is INS Aridhaman?
A. INS Aridhaman is India’s third Arihant-class nuclear-powered ballistic missile submarine (SSBN). It is being built under the Advanced Technology Vessel project at Visakhapatnam.
Q.When will INS Aridhaman be commissioned?
A. The submarine is in sea trials and is expected to be commissioned into service around 2025.
Q.What missiles can INS Aridhaman carry?
A. It has eight SLBM tubes and can carry K-4 (3,500 km) and K-15 (750 km) nuclear missiles. Future K-5 missiles (6,000 km range) are planned.
Q. How is INS Aridhaman different from an attack submarine?
A. Unlike an attack submarine (SSN) designed for conventional warfare, INS Aridhaman’s role is strategic nuclear deterrence. It carries nuclear-capable SLBMs and ensures second-strike capability, whereas an SSN carries torpedoes/cruise missiles for tactical missions.
Q. Why is INS Aridhaman strategically important?A. It completes the sea leg of India’s nuclear triad, providing a hidden second-strike platform. Its stealth and endurance make India’s deterrent credible under the no-first-use policy.
INS Aridhaman embodies a major advance in India’s strategic maritime capabilities. As a nuclear-powered SSBN with enhanced missile load and range, it greatly strengthens India’s sea-based deterrent. Commissioning this boat will ensure India maintains a survivable second-strike force, a cornerstone of its no-first-use doctrine. The submarine also reflects India’s growing indigenization in defense technology (most systems built domestically). For UPSC aspirants, understanding INS Aridhaman involves key GS topics like nuclear doctrine, maritime security, and defense R&D. Its development (and support infrastructure like Project Varsha) will shape India’s strategic posture in the Indo-Pacific for years to come.
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