Indian Navy Accepts Fifth Scorpene, DRDO AIP Targeted For 2024

The Indian Navy’s precarious submarine strength got a boost with the delivery of the fifth Kalvari class Scorpene submarine Vagir on December 20, 2022. With Project-75I in troubled waters the Navy is expected to face a shortfall in capabilities. Air Independent Propulsion (AIP) plugs are planned to boost the capabilities of the Scorpenes in the coming years.

Vagir was launched on November 12, 2020. The submarine was built by Mazagon Docks Limited (MDL) and conducted its first sea sortie on February 12, 2022. Vagsheer, the sixth and final submarine of the class, was launched on April 20, 2022 and is expected to be ready for induction in 2022. The first four submarines Kalvari, Khanderi, Karanj and Vela have been commissioned into the Indian Navy.

The Defence Research and Development Organisation (DRDO) is proceeding with the development of an AIP system. The effort is helmed by the Naval Materials Research Laboratory (NMRL) of DRDO. It is a fuel cell AIP based on phosphoric acid. The PAFC uses hydrogen or methanol reformed gas as fuel. Liquid oxygen is stored onboard while hydrogen is generated on demand.

DRDO AIP plug (Adithya)

The system is modular and can be scaled up to 500kW. The system can also be used for land based power applications in high altitude areas. Each individual stack can produce up to 15kW. The PAFC system is currently built for the Kalvari class submarines as per requirements of the Indian Navy.

The land based prototype and technology has been proven to the Indian Navy. NMRL is also looking to make more scaled prototypes. Larsen and Toubro has been handed the technology for the PAFC AIP. Safety clearance has been obtained from the Naval Group which designed the Scorpenes.

INS Kalvari is slated for refit in the latter half of 2024. Currently, design is being targeted to insert the AIP plug during this refit. Various power configurations are possible since the AIP is modular. Additional endurance of two weeks can be expected from the system depending on use conditions.


The system can be adapted for other classes of submarines. This is significant as reports indicated DRDO might get a Kilo class submarine testbed from the Indian Navy. A requirement for sea proven AIP imposed by the Navy for Project-75I has diminished the possible contenders for the program.

It remains uncertain whether the Navy will allow NMRL to work directly on INS Kalvari without proving the AIP system at sea. However, the eventual installation of the AIP as well as impending use of Li-ion batteries will improve the capabilities of Indian submarines by a considerable margin.