NEW DELHI — An Indian defense laboratory and French company Naval Group are teaming up to integrate fuel cell-based air-independent propulsion systems in Kalvari-class submarines.

As part of the agreement made on Monday between Naval Materials Research Laboratory and Naval Group, the latter will certify the AIP design. The AIP system, which the lab has already developed, will improve the endurance of India’s diesel-electric submarines, the India Defence Ministry said in a statement.

AIP technology is known to enhance the endurance of conventional, or non-nuclear, submarines from about 24 hours to 14-21 days. The Indian Navy has decided to equip all six Kalvari-class submarines with the lab-designed AIP system when the boats undergo their first major refits, with the first planned for two years from now.

The lab, which is part of the government’s Defence Research and Development Organisation, is currently conducting research on strategic materials for the Navy. According to DRDO, efforts involve developing an optimized design for a phosphoric acid fuel cell system, hydrogen generators, power conditioners, control systems, heat exchangers, a demineralization water system, and auxiliaries for the AIP system.

India’s largest private defense contractor, Larsen & Toubro, will serve as prime contractor for the AIP systems, while another private company, Thermax, will supply fuel cells. The Navy has not previously ordered AIP systems from domestic prime contractors.

DRDO declined to comment on the cost of developing the technology.

To date, the Indian government has only tested AIP prototypes, which have successfully met design requirements.

The prototype designs are advanced because the system onboard the submarine uses the chemical sodium borohydride, which mitigates risk since hydrogen is not carried or stored, which is the case with other AIP systems, according to retired Indian Navy Commodore Mukesh Bhargava. The storage of hydrogen — a flammable element — onboard a submarine carries with it the risk of an explosion.

Also on Monday, the Indian Navy commissioned its fifth Kalvari-class submarine INS Vagir. The service said this submarine type features advanced stealth technology and is equipped with long-range guided torpedoes and anti-ship missiles.

The state-run Mazagon Dock Shipbuilders Ltd. in India builds the subs in collaboration with Naval Group.

Vivek Raghuvanshi is the India correspondent for Defense News.

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