Mazagon Dock Shipbuilders Ltd (MDL), a premier Indian public sector shipyard, has entered a formal partnership with the French defence firm Naval Group to upgrade the Indian Navy’s Kalvari-class submarines through integration of an indigenous energy system developed by India’s Defence Research and Development Organisation (DRDO).

The agreement, signed in July 2025, involves the transfer of technology and collaboration to install DRDO’s propulsion modules into the submarines via a sophisticated shipyard process known as "Jumboisation."

This process consists of precision cutting of the submarine's hull, insertion of the energy system plug, and meticulous reassembly to maintain the vessel’s structural integrity and operational readiness.

Naval Group, which originally designed the Scorpene-class submarines that the Kalvari class is based upon, will provide critical technical support throughout the modification.

This includes supplying proprietary components, detailed technical oversight, and specialised training to MDL engineers, ensuring the seamless integration of the indigenous propulsion technology with the existing platform. MDL will lead the integration work on Indian soil, underscoring the collaboration’s mutual reliance on expertise from both parties.

This initiative is part of a larger defence modernization effort by the Indian Ministry of Defence focused on enhancing the submarine fleet’s performance and capability.

In December 2024, the Ministry issued two significant contracts totalling approximately ₹2,867 crore (~$335 million). One contract valued at ₹1,990 crore was awarded to MDL for the construction and integration of the air-independent propulsion (AIP) plug, which significantly extends underwater endurance. A second contract of ₹877 crore was signed with Naval Group for integrating an advanced electronic heavyweight torpedo system, co-developed with DRDO, intended to upgrade the submarines’ firepower.

MDL, located in Mumbai, has a storied legacy dating back to 1774, evolving from a ship repair yard into India’s foremost warship and submarine builder. It has successfully constructed over 805 vessels, including 30 warships and eight submarines, and played a pivotal role in the Project 75 program, which delivered six Scorpene-class submarines through technology transfer from Naval Group.

This current project continues MDL’s critical role in enhancing India’s maritime defence self-reliance under the ‘Atmanirbhar Bharat’ initiative, blending indigenous R&D with proven foreign platforms.

Senior officials from both organisations expressed confidence in the partnership: SB Jamgaonkar, Director of Submarines at MDL, highlighted the teamwork aimed at the successful integration of DRDO’s propulsion system into the submarines, while Laurent Espinasse, Executive Vice President for Submarines at Naval Group, described the collaboration as a significant step forward in operational and technological advancement and a testament to the strong Indo-French strategic defence ties.

In sum, this cooperative venture between Mazagon Dock Shipbuilders Ltd and Naval Group is a landmark advancement in upgrading the Indian Navy’s Kalvari-class submarines.

It enhances the fleet’s underwater endurance, combat effectiveness, and indigenisation of defence technology through a carefully managed process of hull modification and integration of DRDO’s indigenous energy modules backed by French technical expertise.

This project solidifies MDL’s status as a cornerstone of India’s naval capability development and reflects growing strategic collaboration between India and France in the defence sector.

Agencies