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Indian Navy is poised to significantly enhance its underwater combat capabilities by installing an indigenously developed Air-Independent Propulsion (AIP) system on INS Khanderi, the second Kalvari-class submarine, by the end of 2026. Furthermore, all six Kalvari-class (Scorpene) submarines are scheduled to be retrofitted with a fuel-cell-based AIP system developed by the Defence Research and Development Organisation (DRDO).
Senior defence sources said the system, developed by DRDO, has completed extensive shore-based trials and is ready for integration.
“The system has undergone extensive shore-based trials and met the required benchmarks. Integration work on the second submarine is expected to be completed before December 2026,” a senior official familiar with the programme said.
A senior DRDO official confirmed that the crucial “energy module” will soon be handed over to Mazagon Dock Shipbuilders Limited (MDL) for installation. “We will be handing over the energy module system to MDL in the next three to four months,” the official told Asianet Newsable English.
The module will be installed inside the submarine’s hull during a scheduled refit when INS Khanderi will be docked at the Mumbai shipyard.
Sources said sea trials of the upgraded submarine are expected to begin between July and August 2027, with the refit likely to be completed by early 2028.
The indigenous AIP system was originally intended for installation on INS Kalvari, the lead submarine of the six-boat Kalvari class. However, delays in the development programme meant the technology was not ready when the submarine entered service.
The AIP module has been developed by DRDO’s Naval Materials Research Laboratory in Pune using phosphoric acid fuel-cell technology. Officials say the development marks a major step forward in India’s efforts to build critical underwater propulsion technologies domestically.
AIP technology allows conventional diesel-electric submarines to remain submerged for far longer periods without surfacing to recharge batteries. While conventional submarines must snorkel every 4 to 5 days, increasing the risk of detection, submarines equipped with AIP can stay underwater for several weeks, greatly enhancing stealth and operational endurance.
The fuel-cell-based system is also environmentally friendly, producing only water as a by-product, which can be safely discharged into the sea.
The Kalvari-class submarines were built in India at Mazagon Dock Shipbuilders Limited under technology collaboration with France’s Naval Group as part of the Indian Navy’s Project-75 programme. All six submarines of the class have now been commissioned.
The Indian Navy currently operates 16 conventional submarines. Apart from the six Kalvari-class boats inducted over the past decade, most of the remaining submarines are more than 30 years old and nearing retirement, underscoring the need for capability upgrades and new acquisitions for the underwater fleet.
Team BharatShakti
