The Indian Navy's efforts to enhance the stealth and endurance of its Scorpene-class submarines have encountered delays, primarily due to the delayed development of the indigenous air independent propulsion (AIP) system by the Defence Research and Development Organisation (DRDO).

INS Kalvari, the first of the Scorpene submarines built at Mazagon Docks (MDL) with French collaboration, will complete its ongoing maintenance refit at the Mumbai naval dockyard without the planned AIP retrofit. Sources indicate that the DRDO's fuel cell-based AIP system is not yet operationally available. The Navy hopes it will be ready by the time INS Khanderi, the second Scorpene submarine, undergoes its scheduled maintenance in mid-2026.

Indigenous AIP System Delay

The delay in the indigenous AIP project is a major concern, as it was initially slated for completion by June 2017 after being sanctioned in 2014 with an initial cost of ₹270 crore. The AIP system is crucial for enhancing the underwater endurance of diesel-electric submarines, which otherwise need to surface or snorkel regularly to recharge their batteries.

Agreement for AIP Integration

Despite the delays, MDL and Naval Group signed an agreement on July 23 for integrating the indigenous AIP system plugs on the Scorpene submarines. This "jumboisation" project involves cutting the hull, inserting the AIP plug, and rejoining the structure.

Project 75(I) and Scorpene Submarines

Project 75 India (P-75I), envisioned in 1998, aims to acquire six new conventional diesel-electric submarines with AIP technology. The Indian Navy also plans to induct three additional Scorpene submarines. These submarines are intended to bridge the capability gap amid delays in Project 75(I). The contract for these additional Scorpene submarines is still awaiting government clearance, although cost negotiations have concluded.

Enhanced Capabilities of New Scorpene Submarines

The new Scorpene submarines are expected to be larger and more capable than the existing six, with nearly double the mission endurance due to design improvements. These improvements include larger accommodations, increased food and water storage, and expanded sanitary and oil storage facilities. The new submarines will also carry more than twice the weapon load and are designed to accommodate additional weapons in the future. They will feature modernised electric propulsion motors for lower power consumption and quicker maintenance. The diesel generators will be sourced from a different company, reducing fuel consumption by 20 percent and lowering vacuum build-up during snorting operations. The new design will also reduce the submarine's infrared signature, gas volume, and visual footprint, improving stealth.

Indigenous Content

The first six Scorpene submarines had an indigenous content of less than 30 percent. The new submarines are planned to meet the 60 percent indigenous content requirement, with many components made in India. This is expected to encourage French suppliers to strengthen their presence in India, improving the submarines' serviceability.

Strategic Implications

The delays in the AIP retrofit and the P-75I project have strategic implications, as Pakistan and China are modernizing their submarine fleets. The additional Scorpene submarines are seen as a critical measure to address capability gaps.

Shift in Submarine Acquisition Program

The Indian Navy is considering procuring nine state-of-the-art submarines under Project 75(I) from Germany's ThyssenKrupp Marine Systems (TKMS). This could impact plans to expand the current Kalvari-class fleet, as there is a growing consensus that the Scorpene platform represents an older generation of submarine design. The submarines acquired under the P-75(I) project are required to have superior stealth and a proven AIP system from the start.

Despite these challenges, India is committed to enhancing its submarine capabilities through indigenous development and international collaborations. The integration of Indian-designed combat management systems and other advanced systems will enhance operational sovereignty and cyber defence protocols.