India is intensifying efforts to build a robust indigenous submarine force as part of its long-term maritime strategy. With progress on both conventional and nuclear-powered platforms—including the long-delayed Project-75I and the classified SSN program—the Indian Navy is pushing to reduce dependence on foreign suppliers while enhancing undersea deterrence capabilities.
Project-75I: Conventional Submarine Program Reboots with New Momentum
The Project-75 India (P-75I) program—an ambitious plan to build six advanced diesel-electric attack submarines (SSKs) with Air Independent Propulsion (AIP)—has gained renewed traction after years of delays. In September 2025, India’s Ministry of Defence (MoD) approved revised procurement guidelines aimed at breaking the impasse caused by stringent technology transfer requirements that had deterred foreign OEMs.
Originally launched in 2007 under the Strategic Partnership (SP) model, P-75I seeks to pair an Indian shipyard with a foreign technology partner. The contenders include:
- Mazagon Dock Shipbuilders Limited (MDL) – Partnering with Germany’s Thyssenkrupp Marine Systems (TKMS), offering the Type 214 design.
- Larsen & Toubro (L&T) – Teaming up with Spain’s Navantia to propose the S80 Plus variant.
DCNS/Naval Group of France withdrew from the competition in early 2023 citing incompatibility between India’s AIP demands and French IP policies. South Korea’s DSME also exited due to concerns over liability clauses.
The revised Request for Proposal (RFP), expected by late 2025 or early 2026, will reportedly ease some liability conditions while retaining core requirements such as:
- Indigenous AIP integration
- Vertical Launch System (VLS) for cruise missiles
- Minimum endurance of 50 days
This makes P-75I one of the most technically demanding conventional submarine acquisition programs globally. The total projected cost exceeds ₹43,000 crore (~USD $5.2 billion).
Air Independent Propulsion: DRDO’s Fuel Cell System Reaches Maturity
A critical enabler for P-75I is India’s indigenous AIP system developed by the Defence Research and Development Organisation (DRDO). Based on phosphoric acid fuel cell technology, DRDO’s AIP has completed land-based trials and is slated for sea trials aboard a Kalvari-class submarine during its first refit cycle around 2026–27.
The system promises submerged endurance enhancement from ~3–4 days to over two weeks without snorkeling—a significant tactical advantage in contested littoral zones such as the Arabian Sea or Bay of Bengal.
If successful, this would position India among a select group of nations—Germany, Sweden, South Korea—with operational fuel-cell-based AIP systems. DRDO aims not only to integrate it into future P-75I boats but also retrofit it into existing Kalvari-class submarines during mid-life upgrades post-2030.
Nuclear Attack Submarine Program (SSN): Design Phase Nearing Completion
Parallel to conventional efforts, India continues quiet but steady work on its classified program to build six nuclear-powered attack submarines (SSNs). The project was greenlit by India’s Cabinet Committee on Security in early 2015 with an estimated budget exceeding ₹90,000 crore (~USD $11 billion).
The SSNs are being designed by the Directorate of Naval Design (Submarine Design Group) in collaboration with Bhabha Atomic Research Centre (BARC) for reactor development. Industry sources indicate that preliminary design work is complete as of mid-2025 and detailed design is underway at the Secretive Ship Building Centre (SBC) in Visakhapatnam.
The first steel-cutting for hull fabrication is expected by late 2026 or early 2027 at L&T’s Hazira facility—a key industrial partner alongside MDL and BHEL. These SSNs will likely displace around 6,000 tons submerged and be armed with torpedoes and BrahMos cruise missiles via VLS cells or torpedo tubes.
Arihant-Class Update: Strategic Deterrent Force Expands Slowly
The Arihant-class ballistic missile submarines (SSBNs)—India’s sea-based nuclear deterrent cornerstone—are progressing slowly but steadily. INS Arihant has been operational since late 2018; INS Arighat reportedly entered limited service trials in late 2023 though official commissioning remains unconfirmed as of September 2025.
A third hull is under construction at SBC Visakhapatnam while a fourth unit—possibly enlarged—is believed to be laid down. These vessels are powered by an ~83 MW pressurized water reactor derived from Russian assistance but increasingly indigenized through BARC-led efforts.
This strategic force complements India’s no-first-use doctrine under its Nuclear Triad; however, limited patrol endurance (~70 days), low missile loadout (~12 K15 or four K4 SLBMs), and slow production rates remain constraints compared to Chinese Type 094/096 or US Ohio-class equivalents.
Industrial Base Challenges and Opportunities
A persistent bottleneck across all submarine programs remains India’s underdeveloped naval industrial base. While MDL has experience building Scorpène-class boats under license from Naval Group—with five delivered and sixth undergoing sea trials—it lacks capacity for parallel builds across multiple classes without major infrastructure upgrades.
L&T brings modular construction expertise via its work on ATV/SSBN projects but lacks full-cycle production experience for conventional submarines. The government has encouraged private sector participation through SP model reforms but bureaucratic delays continue to hinder progress.
Key challenges include:
- Limited domestic metallurgy capabilities for high-yield pressure hull steel
- Sparse Tier-II/Tier-III vendor ecosystem for marine-grade systems
- Bureaucratic inertia in procurement approvals
- Siloed R&D between DRDO labs lacking integration pathways into production lines
Strategic Implications in Indo-Pacific Context
The acceleration of India’s indigenous submarine capability comes amid rising Chinese naval assertiveness across the Indo-Pacific region. The PLA Navy operates over a dozen nuclear-powered submarines—including six Jin-class SSBNs—and more than four dozen diesel-electric boats including Yuan-class SSKs equipped with Stirling AIP systems.
Pakistan too has contracted eight Hangor-class SSKs from China based on Type 039B design; four will be built at Karachi Shipyard starting mid-decade. This underscores an urgent need for India not only to expand numbers but also field next-generation technologies like AIP propulsion and VLS-launched land attack missiles aboard stealthy platforms capable of extended deployments.
Outlook: Toward Self-Reliance But With Cautionary Optimism
The convergence of political willpower under “Atmanirbhar Bharat” policy thrusts and maturing domestic R&D offers cautious optimism that India may finally overcome decades-long hurdles in building sovereign underwater capability across both conventional and nuclear domains.
Pacing challenges remain—from budgetary constraints to workforce skill gaps—but if execution aligns with planning milestones over this decade, India could emerge as one of few nations fielding both advanced SSKs with indigenous AIP systems and domestically designed SSNs within a single generation cycle—a major leap toward maritime strategic autonomy.
