A contract has been signed between Larsen & Toubro (L&T) and the Defence Research and Development Organisation (DRDO) for the re-fitting of two Air Independent Propulsion (AIP) System modules for the Indian Navy’s Kalvari class of submarines.

These modules make up the heart of the AIP System, which uses fuel cells and is essential for extending the range of conventional submarines. According to the major private defence maker, it was developed domestically by the DRDO’s Naval Materials Research Laboratory (NMRL) with L&T serving as the primary industrial partner on Thursday.

“The energy modules (EMs) comprising fuel cells produce the required power, along with on-board Hydrogen generation. The technology of this indigenous AIP system is a unique one that generates hydrogen on demand thereby obviating the need for carrying hydrogen onboard which is a major safety concern for a submarine,” read the L&T statement.

The contract documents were signed and exchanged last week between Arun T Ramchandani, Executive Vice President and Head-L&T Defence and PT Rojatkar, Director, Naval Materials Research Laboratory (NMRL) of the DRDO. JD Patil, Member of Executive Committee of Management and Advisor (Defence & Smart Technologies) to CEO and MD Larsen & Toubro Ltd and senior officials from NMRL were also present at the event.

The innovative work of the DRDO and L&T to create the AIP system domestically has elevated India into an exclusive club of two nations—South Korea and Germany—that have their own modules. “We are honoured to be the DRDO’s longest-standing development partner across programmes in a variety of fields. Arun Ramchandani commented on the core technology project, which took shape over 12 years of R&D by the DRDO. “L&T is privileged to be associated with realising the dream of realising an indigenous AIP system and mark India’s joining a select group of few nations who have developed the requisite technology. In 2021, it gave the L&T the technology.

JD Patil, a representative of L&T, explained the terms of the agreement by saying, “We are expected to deliver two AIPs in less than two years, and one of them will be refitted on a Kalvari class of submarine built by Mazagon Dock Shipbuilders Limited (MDL) for Navy.”

According to sources, the other AIP would be navalized for DRDO’s future R&D since the current module has only been successfully tested on the ground. Five Kalvari class diesel-electric submarines, including the INS Kalvari, INS Khanderi, INS Karanj, INS Vela, and INS Vagsheer, have already been completed by MDL, and a sixth is now under construction as part of the ’75 India’ project.

Early 2026 would mark the conclusion of a Navy submarine’s first refit cycle, providing an opportunity to integrate EMs into the AIP Plug on the maritime platform.

The business said that L&T’s AM Naik Heavy Engineering Complex in Surat will be used for the manufacturing, integration, and factory acceptance trials of the EMs. “This project would open the door for future orders for AIP Systems to supply the final five Kalvari Class submarines. Other nations that operate Scorpene class submarines may now have more export options, according to L&T.