India is on the cusp of a major milestone in its nuclear deterrent capability, with the Indian Navy confirming that INS Aridhaman, the country’s third indigenously-built nuclear-powered ballistic missile submarine (SSBN), has entered the final phase of harbour and sea trials and is expected to be commissioned “very soon.” Navy Chief Admiral Dinesh K. Tripathi made the announcement at the annual pre-Navy Day press conference, stating that the submarine’s induction will significantly strengthen India’s sea-based nuclear triad at a time of growing maritime competition in the Indo-Pacific.
With the commissioning of Aridhaman—designated S4 / SSBN 82—India will, for the first time, have three operational Arihant-class SSBNs at sea: INS Arihant, INS Arighaat, and the new platform. The development marks the most substantial expansion of the country’s strategic deterrent since the Arihant’s entry into service in 2016.
INS Aridhaman has been under construction for nearly a decade. Built at the Ship Building Centre (SBC) in Visakhapatnam under the long-running Advanced Technology Vessel (ATV) programme, the submarine was quietly launched on November 21/23, 2021 and has since undergone extensive harbour acceptance tests and sea trials.
According to defence officials, the submarine completed its final reactor and weapons integration checks by mid-2025, allowing the Navy to progress to pre-commissioning evaluations this year. The commissioning timeline aligns with earlier military assessments from early 2025, which had projected the submarine’s induction within the year.
Aridhaman follows INS Arighaat, commissioned into the Strategic Forces Command (SFC) on August 29, 2024, after a prolonged cycle of upgrades and weapon trials.
The INS Aridhaman displaces roughly 6,000 tonnes surfaced and around 7,000 tonnes submerged, placing it in the mid-weight SSBN category. The vessel carries a complement of 95–100 crew, including officers and enlisted personnel trained in nuclear propulsion and submarine warfare.
Power comes from an 83 MW CLWR-B1 compact light-water reactor, derived from the prototype naval reactor at Kalpakkam. This drives a single-shaft, seven-blade propeller, enabling speeds of 12–15 knots surfaced and around 24 knots submerged. Its endurance is limited mainly by food and crew cycles rather than fuel, supporting months-long patrols typical of strategic deterrent missions.
The hull is believed to be fabricated from special low-carbon steel, with some open-source assessments indicating the use of anechoic tiles for acoustic suppression. The submarine’s sensor suite includes the USHUS sonar, the Panchendriya unified sonar and tactical control system, bow and flank arrays, and a towed array sonar, collectively enabling long-range detection and tracking in the Indian Ocean’s complex acoustic environment.
Once commissioned, Aridhaman will be based at INS Varsha, the nuclear submarine enclave at Rambilli near Visakhapatnam, and will operate under the Strategic Forces Command as part of India’s nuclear command and control framework.
The submarine’s defining improvement over earlier Arihant-class boats is its expanded missile payload capacity. While INS Arihant and INS Arighaat both feature four vertical launch system (VLS) tubes, INS Aridhaman incorporates eight VLS tubes, doubling the nuclear payload capacity.
This configuration allows the platform to carry:
Up to 24 K-15 Sagarika SLBMs (range ~750 km), or
Up to 8 K-4 SLBMs (range ~3,500 km), or
A future loadout of K-5 SLBMs (estimated range 5,000–6,000 km), currently under development.
The missile options give India flexible deterrence across multiple strategic theatres. The K-15 can target most critical sites in Pakistan from coastal patrol zones, while the K-4 enables reach across the Indian Ocean Region, including areas beyond Southeast Asia. The upcoming K-5 is expected to give India a true long-range sea-based second-strike capability.
Aridhaman is also equipped with six 533 mm torpedo tubes capable of firing Varunastra heavyweight torpedoes, anti-ship cruise missiles, and naval mines for local defence.
Aridhaman’s commissioning will be another critical step in a decades-long journey that began with the strategic dilemmas India faced during the 1971 Indo-Pakistan War, when the US Navy’s Task Force 74 sailed into the Bay of Bengal, trailed by a Soviet nuclear submarine. The episode underscored for Indian planners the need for an assured sea-based deterrent.
Following India’s first nuclear test in 1974, Project 932 examined indigenous nuclear propulsion concepts. The effort matured after the 1998 nuclear tests and India’s formal adoption of a No-First-Use policy, which placed the emphasis squarely on survivable second-strike capabilities.
The ATV programme, costing about ₹900 billion, has since overseen the development of all domestic SSBNs and accompanying infrastructure. The prototype reactor S1 at Kalpakkam reached criticality in 2003 and became operational in 2006, forming the basis of the Arihant-class propulsion system.
Industrial participation is spread across major Indian firms:
L&T for submarine hull and structural engineering
Tata Power SED for control systems
Walchandnagar Industries for steam turbines
Hindustan Shipyard Ltd. for submarine assembly, upgraded in 2009 specifically for nuclear submarine work
INS Arihant (S2) was laid down in 2004, launched in 2009, and inducted in 2016 after a lengthy trial programme. It completed India’s first deterrence patrol in November 2018. INS Arighaat (S3), laid down in 2009 and launched in 2017, was commissioned in 2024 after upgrades and extensive weapon testing.
A fourth unit, S4*, was launched on October 16, 2024, and will carry only K-4 missiles. The S4 and S4* variants are about 10 metres longer than Arihant and Arighaat, following a 2007 design revision to increase their missile load without waiting for the larger S5 class.
India ultimately plans to field three larger S5-class SSBNs, each displacing around 13,500 tonnes and carrying much longer-range submarine-launched ballistic missiles. Preliminary design and internal studies are ongoing.
In parallel, India has signed a $3 billion lease agreement for a new Russian-built Akula-class nuclear attack submarine (Chakra III), slated for delivery around 2028.
Separately, the Project 77 indigenous SSN programme, approved by the Cabinet Committee on Security in October 2024, aims to construct six 10,000-ton nuclear attack submarines designed by the Navy’s Warship Design Bureau.
India’s naval expansion mirrors rising security challenges in the Indo-Pacific. As of December 2024, the Navy operated over 130 warships and 251 aviation assets, with plans to reach 155–160 vessels by 2030, 175–200 by 2035, and up to 230 warships and submarines by 2037.
By late 2025, 54 ships were under construction across Indian shipyards, with 10 slated for commissioning this year alone. The Defence Acquisition Council has cleared 74 additional warships, valued at around ₹2.35 lakh crore ($26 billion).
Aridhaman’s commissioning comes amid heightened Chinese naval activity in the Indian Ocean Region, including regular deployments of PLAN submarines and survey vessels. To counter this, India has enhanced its anti-submarine warfare posture with:
Kamorta and Mahe-class corvettes
P-8I Poseidon long-range maritime patrol aircraft
Saryu-class patrol vessels
Heron-1 UAVs, among other assets
Simultaneously, infrastructure upgrades are underway across the Andaman & Nicobar Islands and Lakshadweep, creating a network of forward operating bases supporting surveillance and rapid deployment.
India is also progressing multiple diesel-electric submarine programmes, including:
Three more Kalvari-class submarines or a modified Type-214 design
Six Project 75-I AIP-equipped submarines, based on an enlarged Type-214
Twelve Project 76 AIP submarines with land-attack cruise missiles
Five midget submarines for MARCOS operations
Twelve Extra-Large Unmanned Underwater Vehicles (XLUUVs) worth ₹2,500 crore
The indigenous Jalkapi XLUUV, whose construction began in June 2025
With INS Aridhaman set for commissioning, India’s nuclear triad is entering a more resilient and distributed phase. For the first time, the country will be able to maintain continuous at-sea SSBN patrols, a critical requirement for credible minimum deterrence.
