In 1998, India planned 24 submarines by 2030, currently it has 16 and newest submarines are years away

India’s conventional submarine fleet is facing a widening capability gap as ageing vessels are retired faster than new submarines can be inducted, while major replacement and expansion programmes remain years away from delivering additional boats. The Indian Navy currently operates 16 conventional diesel-electric submarines across the Kalvari, Sindhughosh and Shishumar classes, alongside three strategic submarines, but its target of inducting 24 conventional submarines by 2030 has fallen behind schedule.

Four Sindhughosh-class submarines have already been retired, including INS Sindhughosh, the lead vessel of the class. Although six Kalvari-class Scorpene submarines have entered service and the Shishumar-class fleet has undergone mid-life upgrades, the latter vessels are around 35 years old on average. With more older submarines due to retire in the coming years, the Navy faces mounting pressure to replenish its underwater combat capabilities.

India is pursuing several parallel initiatives to address the shortfall, including Project 75I for foreign-designed submarines built in India, an indigenous conventional submarine programme, plans for nuclear-powered attack submarines and a proposed lease of a Russian nuclear-powered attack submarine. The Navy expects to acquire at least 22 domestically built submarines through these programmes, but the timelines mean the fleet will not expand immediately.


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India’s submarine fleet: An ageing force and delayed expansion

India’s submarine modernisation effort was guided by a 30-year construction plan drawn up in 1998 by Vice Admiral AK Chatterji. It envisaged parallel foreign and domestic submarine-building programmes, with the objective of expanding the fleet by 2030.

However, the ambition has fallen well behind schedule. The retirement of four Sindhughosh-class boats has reduced the conventional fleet, while the six Kalvari-class submarines inducted so far have not been sufficient to meet the planned expansion. The Shishumar-class submarines have received mid-life upgrades, but their average age of around 35 years highlights the challenge of relying on older platforms as replacement programmes progress.

The gap is particularly significant because submarine construction and induction take years. Even projects that move through technical evaluation and contract negotiations must pass through construction and testing before new boats can enter service.

Project 75I: India’s biggest conventional submarine procurement effort

Project 75I is among the most significant efforts to strengthen the conventional submarine fleet. The procurement programme is valued at around ₹70,000 crore and envisages the acquisition of six to nine submarines.

Mazagon Dock Shipbuilders and Germany’s Thyssenkrupp Marine Systems (TKMS) have cleared the technical evaluation stage. India is moving towards final cost negotiations for at least six Type 214 submarines equipped with air-independent propulsion (AIP).

However, the project is unlikely to provide an immediate solution to the fleet shortfall. The first submarine is expected around seven years after the contract is signed, meaning the benefits will materialise only over the longer term.

India is also working to expand domestic manufacturing of submarine weapons. Hyderabad-based VEM Technologies has signed an agreement with TKMS to manufacture heavyweight torpedoes in India, supporting efforts to develop the local industrial base for undersea warfare.

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Project 76: Indigenous conventional submarines planned

Project 76 is expected to follow as an indigenous conventional submarine programme. The proposed submarine family is expected to incorporate a modified version of the air-independent propulsion system developed by the Defence Research and Development Organisation (DRDO).

The programme is part of India’s broader effort to build more submarines domestically rather than depend entirely on foreign-designed platforms. Its eventual contribution to the fleet will depend on the programme’s development and induction timelines.

AIP technology: Why it matters for conventional submarines

Air-independent propulsion is an important capability for conventional diesel-electric submarines because it allows them to remain submerged for two to three weeks without surfacing or snorkelling to recharge their batteries.

Submarines without AIP need to snorkel more frequently, increasing the risk of detection by aircraft and surface vessels. Remaining submerged for longer periods can improve a conventional submarine’s ability to operate without revealing its position.

Of India’s existing conventional submarines, only the six Kalvari-class boats are slated to receive a DRDO-developed AIP system. Project 75I submarines are also expected to feature AIP, while the proposed Project 76 family is expected to use a modified DRDO-developed system.

Project 77: Nuclear-powered attack submarines

Alongside conventional submarine procurement, the Navy is pursuing nuclear-powered attack submarines under Project 77. The Cabinet Committee on Security has approved two such submarines, with a reported cost of ₹35,000 crore.

The first submarine is expected by 2036-37, placing the programme well beyond the immediate period in which the Navy needs to replace ageing conventional boats.

The Navy is also planning to lease a nuclear-powered attack submarine from Russia to strengthen its capabilities in the interim. The proposed lease is intended to provide an additional capability while domestic nuclear-powered submarine programmes advance.

Strategic submarines and the nuclear triad

India’s strategic submarine programme has progressed faster than its conventional submarine expansion plans. INS Aridaman, the third Arihant-class ballistic missile submarine, has strengthened the country’s nuclear triad, which also includes land-based missiles and aircraft.

INS Aridaman is designed to carry up to eight K-4 nuclear-capable missiles, each with a range of 3,500 km. A fourth ballistic missile submarine has been launched at Visakhapatnam, while the larger S-5 class is planned for the future.

Submarines are considered a particularly difficult component of the nuclear triad to track because they can remain concealed deep underwater. Their ability to operate covertly supports a credible nuclear deterrent by preserving the capacity to retaliate even if a country’s land-based assets come under attack.

Strategic submarines, however, serve a different role from conventional diesel-electric attack submarines. The expansion of India’s ballistic missile submarine fleet therefore does not, by itself, resolve the shortfall in conventional underwater combat platforms.

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Why submarines remain a critical military asset

The value of submarines extends beyond nuclear deterrence. Their ability to approach or track surface vessels without being detected can provide a major operational advantage.

Earlier this year, a US submarine reportedly tracked and sank the Iranian frigate IRIS Dena off Sri Lanka without the warship detecting the underwater threat. The episode highlighted the potential vulnerability of surface vessels to submarines operating covertly.

For India, maintaining a sufficiently large and modern submarine fleet is therefore important to sustaining underwater combat capabilities as older vessels retire and new procurement programmes move towards delivery.

How India plans to bolster its submarine numbers

India’s response involves multiple programmes at different stages, from the procurement of foreign-designed conventional submarines to indigenous construction and nuclear-powered attack submarines.

Project 75I is expected to bring in new conventional boats with AIP, while Project 76 is intended to advance indigenous conventional submarine development. Project 77 will add nuclear-powered attack submarines over the longer term, and the proposed Russian lease is intended to provide an interim boost.

The Navy expects to acquire at least 22 domestically built submarines under these programmes. However, with several projects still in procurement or development and the first Project 75I submarine expected around seven years after contract signing, the challenge will be to ensure that new inductions keep pace with the retirement of older boats.