The Kalvari-class is a class of six diesel-electric attack submarines built for the Indian Navy under Project 75, based on the French Naval Group’s Scorpene design. The class gives India a modern, quiet, and combat-capable conventional submarine fleet, closing a significant capability gap after decades of relying on ageing Foxtrot, Kilo, and HDW-derived boats.[1]
Project 75 was formalised through a contract signed on 6 October 2005 between India and France for the licence-built construction of six Scorpene-class submarines in India, under technology transfer from Naval Group (then DCNS). The programme aimed to build indigenous submarine-construction capability at Mazagon Dock Shipbuilders Limited (MDL) in Mumbai while delivering a modern conventional submarine fleet, though the programme suffered significant delays from its originally envisaged timeline.
All six submarines were built by MDL under French technical assistance. The lead boat, INS Kalvari, was commissioned in December 2017, becoming the first in a class that would enter service over the following eight years. The sixth and final submarine, INS Vagsheer, was commissioned in January 2025, completing the class’s full induction nearly two decades after the original contract was signed.[2]
Each Kalvari-class submarine is approximately 67 metres (220 feet) long, displaces around 1,775 tonnes, and can dive to a maximum operating depth of 350 metres. The boats are capable of speeds of around 20 knots submerged and 11 knots on the surface, and incorporate modular construction techniques intended to simplify future upgrades and mid-life overhauls.[3]
The class is armed with heavyweight torpedoes and Exocet SM39 anti-ship missiles, launched from six 533mm torpedo tubes, giving the boats a potent combination of anti-ship and anti-submarine strike capability. The submarines feature advanced stealth characteristics, including reduced acoustic, magnetic, and radar signatures, along with modern sonar and combat management systems designed to support both open-ocean and littoral operations.
A DRDO-developed indigenous Air-Independent Propulsion (AIP) plug, intended to extend submerged endurance significantly beyond what a purely diesel-electric boat can achieve, has been under development for retrofit onto the class. As of August 2025, the AIP energy module was not yet ready for integration, meaning the lead boat INS Kalvari’s maiden maintenance refit was completed without it. The second submarine, INS Khanderi, is instead set to become the first to receive the AIP system, with a refit scheduled from July 2026, integration expected to take around three months and complete by December 2026, and initial sea trials with AIP projected for July-August 2027.[4]
The Kalvari-class forms the core of India’s modern conventional submarine arm, providing sea-denial, anti-surface, and covert intelligence-gathering capability across the Indian Ocean Region. The programme also established indigenous submarine-construction expertise at MDL that is expected to inform India’s larger and more ambitious Project 75(I) programme, which envisages further conventional submarines with indigenous AIP fitted from build rather than retrofitted.
| Type | Diesel-Electric Attack Submarine (Project 75, Scorpene-class) |
| Builder | Mazagon Dock Shipbuilders Limited, under licence from Naval Group (France) |
| Displacement | ~1,775 tonnes |
| Length | ~67 metres |
| Speed | ~20 knots submerged; ~11 knots surfaced |
| Max Depth | ~350 metres |
| Armament | Heavyweight torpedoes, Exocet SM39 anti-ship missiles (6 x 533mm tubes) |
| Boats in Class | INS Kalvari (2017), Khanderi, Karanj, Vela, Vagir, INS Vagsheer (2025) |
| AIP Status | Indigenous DRDO AIP under integration; first retrofit planned on INS Khanderi (2026) |