The Kalvari-class are diesel-electric attack submarines built for the Indian Navy under Project 75, based on the French Naval Group (formerly DCNS) Scorpene design and constructed in India by Mazagon Dock Shipbuilders Limited (MDL) under a technology-transfer arrangement. Six boats were built — INS Kalvari, INS Khanderi, INS Karanj, INS Vela, INS Vagir, and INS Vagsheer, the last of which was commissioned in early 2025 — giving India its most modern conventional submarine class.[1]
Project 75 was signed in 2005 as a technology-transfer agreement between France’s DCNS (later Naval Group) and MDL, under which Scorpene-class submarines would be built in India rather than imported outright, with roughly 30 percent of each boat — including the pressure hull — fabricated domestically.[2] The programme was intended both to modernise the Navy’s ageing conventional submarine fleet and to build indigenous submarine-construction expertise at MDL for future programmes.
The six-boat build proved slower than originally planned, with the lead boat INS Kalvari commissioning in December 2017, more than a decade after the technology-transfer agreement was signed. Subsequent boats followed at roughly annual intervals: Khanderi (2019), Karanj (2021), Vela (2021), Vagir (2023), and finally Vagsheer, the sixth and last of the class, commissioned in January 2025.[3]
In August 2016, roughly 22,400 pages of technical documentation on the Scorpene design were leaked and published by an Australian newspaper, reportedly sourced from a former French naval officer who had subcontracted for DCNS. The leaked material covered underwater and above-water sensors, the combat management system, torpedo launch specifications, communications, and navigation systems, though it dated to material prepared around 2011 and predated later armament integration.[4] The leak prompted a French judicial inquiry and an India-France joint review of the programme’s security protocols, and while it caused significant diplomatic concern at the time, the Navy and DCNS maintained that no operationally critical current-generation data had been compromised.[5]
The Kalvari-class uses a hydrodynamically optimised hull design derived from the Scorpene family, emphasising a low acoustic signature through advanced anechoic tiles, X-form stern control surfaces for manoeuvrability, and a combat system architecture adapted for Indian Navy requirements. Displacement is approximately 1,550 tonnes surfaced, with a crew of around 8 officers and 35 sailors.[6]
Each boat is armed with six 533mm torpedo tubes capable of firing heavyweight torpedoes and tube-launched Exocet SM39 anti-ship missiles, giving the class a potent anti-ship and anti-submarine strike capability in addition to its primary roles of intelligence gathering, surveillance, and area denial.[6]
A DRDO-developed indigenous Air Independent Propulsion (AIP) system was planned to be retrofitted into the class to extend submerged endurance without needing to surface or snorkel as frequently, a major stealth and survivability enhancement. However, as of 2025-2026 the AIP module has repeatedly missed integration deadlines: INS Kalvari completed a scheduled maintenance refit without receiving the AIP retrofit, and the Navy is now targeting INS Khanderi’s mid-2026 refit as the next opportunity for the first at-sea AIP integration.[7] The AIP module, designed as a roughly 10-metre, 300-tonne plug section, would extend the boats to about 77.5 metres in length and increase displacement to around 2,000 tonnes if successfully retrofitted across the class.[7]
The delays in retrofitting AIP to the existing Kalvari-class have direct implications for the follow-on Project 75(I) programme, under which India plans to build six new, larger conventional submarines with AIP integrated from the outset rather than retrofitted. Difficulties maturing the indigenous AIP system on the Kalvari-class have been cited as a risk factor for Project 75(I)’s own schedule.[7]
Kalvari-class boats operate primarily from the Western Naval Command and are tasked with anti-surface and anti-submarine warfare, intelligence gathering, mine-laying, and special-forces insertion in addition to conventional deterrence patrolling. As India’s most modern conventional (non-nuclear) attack submarines, they form the backbone of the Navy’s diesel-electric submarine fleet alongside the older, Russian-origin Kilo and German-origin Shishumar classes.[8]
Beyond their individual operational value, the Kalvari-class programme significantly expanded Indian submarine-construction capability at MDL, providing the design, tooling, and workforce experience that underpins subsequent submarine programmes, even as the AIP retrofit saga illustrates the continuing challenge of maturing indigenous propulsion technology to keep pace with imported hull and combat-system technology.[2]
| Type | Diesel-Electric Attack Submarine |
| Displacement | ~1,550 tonnes (surfaced) |
| Crew | ~8 officers, 35 sailors |
| Armament | 6 × 533mm torpedo tubes, Exocet SM39, heavyweight torpedoes |
| Design | Naval Group Scorpene (licence-built) |
| AIP Status | Retrofit planned, not yet integrated (as of 2026) |
| Boats | Kalvari, Khanderi, Karanj, Vela, Vagir, Vagsheer |
| Builder | Mazagon Dock Shipbuilders Ltd (with Naval Group, France) |