The Kalvari-class are diesel-electric attack submarines built in India under Project-75, based on the French Scorpene design developed by Naval Group. Constructed at Mazagon Dock Shipbuilders (MDL) in Mumbai, the class marked a major step in transferring modern submarine construction know-how to Indian industry. The boats are quiet, agile conventional submarines optimised for coastal and regional operations, and their induction has substantially renewed the Navy's ageing underwater fleet.

Design and construction

Scorpene-type submarines are designed for stealth, with a low acoustic signature that makes them difficult to detect. They can undertake anti-surface and anti-submarine warfare, intelligence gathering, minelaying and special operations. Armament typically includes heavyweight torpedoes and anti-ship missiles launched through the torpedo tubes, giving the class a potent sea-denial punch against both surface ships and other submarines. Modern sensors and combat management systems allow a small crew to build a detailed picture of the surrounding waters and to prosecute contacts with precision.

Project-75 was executed with technology transfer from Naval Group, allowing MDL to establish the facilities, skills and quality processes needed for serial submarine production. Submarine building is unforgiving: welds must withstand crushing pressure, systems must be exceptionally reliable, and tolerances are exacting. Mastering these disciplines domestically is arguably as valuable as the boats themselves. This industrial capability forms the foundation on which India intends to build more advanced vessels, and the experience gained directly informs the follow-on P-75I programme, which seeks conventional submarines fitted with air-independent propulsion.

Role in the fleet

As conventional attack submarines, the Kalvari-class complement rather than replace India's nuclear boats. Where the Arihant-class provides strategic deterrence and long endurance, the Kalvari boats deliver tactical sea-denial and offensive capability in India's near seas at a fraction of the cost. Diesel-electric propulsion makes them well suited to the littoral, where their quietness while running on batteries is a decisive advantage, allowing them to lie in wait or stalk targets in shallow, cluttered waters.

Within the Indian Navy, these submarines operate alongside surface combatants and aircraft to build a layered picture of the undersea environment. They frequently work in concert with anti-submarine platforms such as the Kamorta-class corvettes and long-range maritime patrol aircraft, either as the hunter or, in training, as the elusive target that sharpens the fleet's anti-submarine skills. A capable submarine force also complicates any adversary's planning, forcing them to devote significant resources to anti-submarine defence.

The class is being inducted progressively, with additional boats and possible follow-on orders discussed as part of sustaining India's underwater strength; specific numbers and timelines remain subject to decision and should be treated as evolving. Each successive boat benefits from lessons learned during the construction and trials of its predecessors, and efforts to further indigenise systems, add air-independent propulsion in future designs and integrate more Indian-made weapons and sensors are expected to continue.

The programme's success has demonstrated that Indian yards can deliver complex, high-quality submarines, reinforcing the self-reliance goals that run through the modernisation of the Navy's warship fleet. Together, the Kalvari boats represent both a capable frontline force and a crucial learning platform for the country's long-term ambition to design and build submarines with ever-greater indigenous content, gradually reducing dependence on foreign designers for one of the most sensitive categories of military hardware. As the Navy balances the induction of new boats against the retirement of older ones, classes such as the Kalvari are central to sustaining an adequate submarine strength through a period of intense modernisation. Their combination of stealth, firepower and proven construction makes them a dependable core of the conventional underwater force, and the industrial knowledge embedded in the programme will continue to pay dividends across successive generations of Indian submarines.