AIP system to boost underwater endurance of India's submarine fleet

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

An AIP allows a conventional diesel-electric submarine like the Kalvari-class to remain submerged for eight to 10 days without the need to surface at sea and recharge its onboard batteries. A submarine without an AIP system needs to resurface every four to five to recharge its batteries.

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

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

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

The Naval group announced a 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 subs are based on the Scorpene-class subs of the Naval Group, the French company will provide technical oversight, proprietary materials and specialised training engineers of the MDL to ensure integration.

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

Laurent Espinasse, Executive Vice-President of Submarine division at Naval Group, said, “The integration of indigenous system into the Kalvari-class submarines is a major step forward in our journey toward technological and operational advancements.”