Navy is pursuing purchase of German made subs from Thyssenkrupp Marine Systems (TKMS)

India is pursuing an ambitious, multi-pronged submarine modernisation program aimed at ensuring maritime dominance, safeguarding national security in the Indo-Pacific, and sustaining a credible sea-based nuclear deterrent well into the 2030s.

This strategic roadmap integrates three major submarine categories—diesel-electric attack submarines (SSKs), nuclear-powered ballistic missile submarines (SSBNs), and nuclear-powered attack submarines (SSNs)—into a unified framework aligned with India’s maritime doctrine of sea denial, sea control, and credible minimum deterrence. The program is shaped by the dual imperatives of countering China’s fast-expanding submarine fleet and Pakistan’s modernising undersea capabilities, alongside the urgent need to replenish India’s ageing conventional submarine strength.

China’s People’s Liberation Army Navy (PLAN) is projected to operate between 65 and 80 submarines by 2030, including nuclear-powered attack and ballistic missile boats, backed by a large fleet of advanced diesel-electric submarines. Regionally, Pakistan—leveraging Chinese technology—continues to upgrade its Agosta-90B fleet and is developing the new Hangor-class series.

Against this backdrop, the Indian Navy’s conventional submarine force has dwindled from 21 boats in the 1980s to just 15 by 2024, many approaching obsolescence. This makes the modernisation program not merely aspirational but an operational imperative to plug immediate capability gaps and build long-term strategic depth.

The conventional submarine segment has seen steady progress under Project-75 (P-75), which delivered six French-designed Scorpène-class boats built indigenously at Mazagon Dock Shipbuilders Ltd (MDL) in partnership with Naval Group.

These modern diesel-electric submarines—equipped for anti-submarine warfare, intelligence gathering, and special operations—were commissioned between 2017 and 2025, with INS Vagsheer joining the fleet in January 2025. The Navy has also proposed building three additional Scorpènes to further stabilise fleet numbers. Parallel life-extension refits of the ageing Shishumar-class (HDW Type 209) submarines, INS Shishumar and INS Shankush, are underway to extend their operational relevance until well into the 2030s.

Indian Navy Submarine Modernisation: 2024–2035 Strategic Roadmap

Refer to the text-based timeline chart showing year-by-year milestones for SSKs (diesel-electric), SSBNs, and SSNs, including build starts, commissioning, and projected inductions.

YearDiesel-Electric SSKs (Project 75 / 75(I) / Upgrades)Nuclear Ballistic Missile Submarines (SSBN)Nuclear Attack Submarines (SSN)
2024INS Arighat commissioned (actually SSBN, not SSK)INS Arighat commissionedWork on indigenous SSNs approved by CCS
2025INS Vagsheer commissioned (6th & last P-75 boat). Negotiations conclude for 3 additional Scorpène boats. Shishumar-class (INS Shishumar, INS Shankush) mid-life upgrades nearing completionINS Aridhaman (S4) undergoing trials, planned commissioningLease of Akula-class SSN from Russia expected late 2025/26
2026Shishumar upgrades complete; additional Scorpène orders expected to begin constructionAridhaman fully operationalRussian leased SSN arrives (bridging capability gap)
2027Work begins on first P-75(I) AIP submarineConstruction start of S-5 class SSBN (13,500t, 12–16 SLBMs)Indigenous SSN detailed design freeze; dry dock and module prep
2028Work continues on P-75(I) lead boat; follow-on hulls begin staggered constructionS-5 build progressesHull fabrication starts for SSN-1
2029Additional Scorpènes under constructionS-5 reactor integration stageSSN-1 build continues
2030Possible commissioning of 1–2 additional ScorpènesS-5 systems outfittingKeel laying for SSN-2
2031Follow-on P-75(I) hulls under constructionS-5 nearing launchSSN-1 outfitting & trials prep
2032First P-75(I) submarine launches for trialsLaunch of S-5; reactor testsSSN-1 sea trials
2033Commissioning of P-75(I) Boat 1S-5 class commissioningSSN-1 commissioned. SSN-2 build continues
2034P-75(I) Boat 2 trials; Boat 3 constructionSecond S5-class laid downIndian SSN-2 sea trials
20352–3 P-75(I) boats commissionedS5-class work continuesSSN-2 commissioned

Looking forward, the next phase in conventional submarine induction is Project 75(I), envisaging six state-of-the-art, air-independent propulsion (AIP) equipped submarines with vertical launch system (VLS) capability for cruise missiles, extended underwater endurance, and high indigenous content. After prolonged delays arising from stringent naval requirements and limited vendor compliance, MDL—partnering with Germany’s Thyssenkrupp Marine Systems (TKMS)—emerged as the sole compliant bidder in early 2025. The build timeline of approximately seven years for the first unit points to a mid-2030s entry into service, with the entire class expected to be delivered during that decade.

On the nuclear deterrence front, India’s SSBN program anchors its sea-based nuclear triad. The lead boat, INS Arihant, commissioned in 2016, is armed with K-15 SLBMs and has been operational since 2018. The second unit, INS Arighat, entered service in 2024 with expanded missile capacity, including the 3,500-km range K-4 SLBM. The third boat, INS Aridhaman, a 7,000-tonne platform with eight missile tubes capable of carrying longer-range K-5 missiles (~6,000 km), is undergoing sea trials and slated for commissioning in 2025. In parallel, India is developing its next-generation S5-class SSBNs, projected at around 13,500 tonnes with a 190 MW reactor and payload capacity for up to 12–16 K-5/K-6 SLBMs with multiple independently targetable re-entry vehicle (MIRV) warheads. Construction of the first S5 is expected to begin by 2027, with a long-term goal of fielding up to six such advanced submarines.

The nuclear attack submarine (SSN) program is another pillar of India’s undersea strategy. Following the end of the INS Chakra III’s lease from Russia in 2021, India is negotiating another Akula-class lease to bridge the gap until indigenous SSNs become operational. The Cabinet Committee on Security approved the construction of the first two wholly indigenous SSNs in late 2024, with a total plan for six boats. Valued at ₹45,000 crore (~USD 5.4 billion) for the initial pair, the first SSN is targeted for delivery by 2036, with a second to follow within two years. These hunter-killer submarines are envisaged as fast, quiet, long-endurance platforms integrating advanced torpedoes, anti-ship and land-attack missiles, and potentially unmanned underwater vehicles for multi-domain operations.

While this modernisation roadmap is comprehensive, it faces challenges. P-75(I) suffered delays due to demanding stealth, endurance, and weapons integration requirements paired with strict technology transfer conditions. Indigenous SSBN and SSN programs require sustained investment, advanced reactor development, and mastery of complex undersea systems. Nevertheless, the government seeks high indigenous content across all platforms in line with the “Make-in-India” policy, gradually reducing dependency on foreign technology and supply chains.

By 2035, India aims to maintain a balanced undersea fleet comprising a triad-capable SSBN force, advanced SSNs for offensive and intelligence missions, and a rejuvenated diesel-electric fleet equipped with AIP and VLS capabilities. Together, these assets are expected to ensure credible deterrence against China and Pakistan, secure India’s maritime approaches, and project power across the Indo-Pacific. This integrated plan combines legacy platform upgrades, interim capability acquisition through foreign collaboration, and the growth of indigenous industrial capacity—cementing the submarine arm as a decisive factor in India’s strategic posture in the evolving maritime security environment.

IDN (With Agency Inputs)