Indian Navy submarine fleet to get Air Independent Propulsion system for greater underwater endurance

The underwater endurance of Indian Navy’s Kalvari-class submarines is set to be increased. The fleet of six submarines will be retro-fitted with a technology called Air Independent Propulsion (AIP) system which allows the submarines to remain under water for longer periods.

An AIP allows a conventional diesel-electric submarine like the Kalvari-class to remain submerged for 8-10 days without the need to surface at sea and re-charge its onboard batteries. A submarine without an AIP system needs to re-surface every 4-5 days to recharge its batteries.

Batteries of the diesel-electric submarine like the Kalvari-class are charged by an onboard diesel engine. Since the exhaust of a diesel engine cannot be discharged under sea, the submarine comes close to sea surface to expel the engine exhaust. At this point, the submarine, considered one of the most potent military platforms, is vulnerable to enemy detection due to heat of the engine exhaust and the noise of the engine that is picked up by sonars of enemy warships.

The AIP allows a sub to remain submerged for longer period, hence cutting down on chances of it being detected.

The Defence Research and Development Organisation (DRDO) had developed an AIP system that is being installed on the subs. The French Naval Group and Mumbai-based Mazagon Dock Shipbuilders Limited (MDL) on Thursday announced to extend their cooperation to support the integration of DRDO’s AIP onto the submarines.

The naval group announced a formal collaboration with the MDL for integrating the ‘indigenous energy system plug’ (the technical name for the AIP). Under this agreement, the submarines will undergo a complex process known as “jumboisation”, involving precision-cutting of the hull, safe insertion of the plug, and re-joining of the structure to have a fully operational and safe submarine.

Since the Kalvari-class submarines are based on the Scorpene-class submarines of the naval group, the French company will provide technical oversight, proprietary materials and specialised training to experienced Indian engineers of the MDL to ensure seamless integration.

In December last year, the Indian Ministry of Defence signed a contract with the MDL for Rs 1,990 crore, for the construction of plug for the DRDO-AIP system and its integration onboard Indian submarines.

A statement of the Naval Group on Thursday said, “This project, reflects the commitment of MDL and Naval Group in supporting India's vision of self reliance in defence manufacturing, contributing significantly to the ‘Aatmanirbhar Bharat’ initiative, with the incorporation of indigenous technologies developed by the DRDO into the Kalvari class submarines”.

Laurent Espinasse, Executive Vice President of the submarine division at the naval group, said, “We are honoured to deepen our partnership with the MDL and the DRDO. The integration of indigenous energy system into the Kalvari-class submarines is a major step forward in our shared journey toward technological and operational advancements.”