India’s Scorpene Submarine AIP Upgrade Faces Fresh Delay, INS Kalvari to Miss Integration

India’s ambitious plan to equip its six Scorpene-class submarines with a homegrown Air-Independent Propulsion (AIP) system has hit yet another setback, pushing the timeline further. The first submarine, INS Kalvari, which was commissioned in 2017, is currently undergoing its scheduled refit but will not receive the AIP system as originally intended. Instead, the integration has now been deferred to the second Scorpene, INS Khanderi, when it enters refit in mid-2026.

The AIP project, based on indigenously developed fuel-cell technology by the Defence Research and Development Organisation (DRDO) in partnership with Larsen & Toubro (L&T), was sanctioned back in 2014 with an allocation of ₹270 crore. Initially, the system was slated for completion by June 2017, in time to be retrofitted on the first submarine during its first major refit. However, technical hurdles, prolonged testing phases, and delays in operational certification have stretched the program well beyond the original timeline.

While recent trials have indicated promising results, the AIP is still not considered ready for full-scale operational deployment. The technology is crucial for conventional diesel-electric submarines, allowing them to remain submerged for extended periods without surfacing to recharge batteries. This significantly enhances stealth, survivability, and combat endurance, especially in contested waters where detection risks are high.

India currently operates six Kalvari-class submarines built at Mazagon Dock Shipbuilders Limited (MDL) under a technology transfer agreement with France’s Naval Group. With increasing Chinese presence in the Indian Ocean and Pakistan also inducting new submarines with advanced propulsion systems, the delays in India’s AIP program raise concerns about maintaining undersea combat edge in the region.

Officials maintain that despite setbacks, the indigenous AIP remains a strategic necessity for self-reliance in critical defence technology. Once integration begins with INS Khanderi, the remaining Scorpene submarines are expected to be gradually upgraded during their respective refits in the coming years.