India’s DRDO-developed Air Independent Propulsion (AIP) system will be installed on INS Khanderi by July 2026. The system, built with L&T and Thermax, will boost submarine endurance, allowing longer submerged operations and reduced detection risk.
New Delhi: The Defence Research and Development Organisation’s (DRDO) indigenously developed Air Independent Propulsion (AIP) system is slated to be fitted on INS Khanderi, the second submarine of the Kalvari-class, by July 2026, a top official in the defence and security establishment said. The AIP system was originally meant for INS Kalvari, the first of the Indian Navy’s six Kalvari-class diesel-electric submarines, but its integration was delayed. The Navy now plans to equip INS Khanderi with the system during its scheduled refit in mid-2026.
Developed in collaboration with industry partners Larsen & Toubro (L&T) and Thermax, the AIP prototype is expected to be ready by December this year. Installation on the submarine will take approximately one year, followed by harbour and sea trials.
“If all goes according to plan, initial sea trials are expected to commence between March and April 2027, with the full refit process expected to conclude by July 2027,” the official added.
All about AIP system
The AIP system is a technology that greatly boosts the underwater endurance of conventional diesel-electric submarines, allowing them to remain submerged for up to two weeks. Internationally, there are different types of AIP systems, but the fuel cell-based AIP is considered to be unique as the hydrogen is generated onboard. It will obviate the requirement of carrying hydrogen onboard, a major safety concern for submarines.
With its integration into the submarines, India will join an elite club of nations that have indigenously developed fuel cell-based submarine AIP technology.
This technology is environmentally friendly, as its only by-product is clean water that can be safely discharged into the ocean.
Without an AIP system, a submarine needs to surface every four to five days to recharge its batteries. With AIP, however, it can remain submerged for much longer, reducing the risk of detection.
Recently, the French Naval Group and Mumbai-based Mazagon Dock Shipbuilders Limited (MDL) had announced their cooperation to integrate DRDO’s AIP onto the submarines, as Asianet News English reported earlier.
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.
As reported by Asianet News English in December 2024, the Indian Ministry of Defence inked a Rs 1,990 crore contract with MDL for the construction of the DRDO-developed AIP system and its integration into submarines.