Setback in AIP Integration for Indian Scorpene Submarines: Delay in INS Kalvari Upgrade Confirmed

National News: The Indian Navy’s ambition to modernize its Scorpene-class (Kalvari-class) submarines with Air Independent Propulsion (AIP) systems has hit another roadblock. The much-anticipated indigenous AIP system, developed by DRDO, is still not operational, delaying its planned installation in the Navy’s first Scorpene submarine, INS Kalvari.

INS Kalvari Upgrade Deferred

Commissioned in December 2017, INS Kalvari was the first submarine built under Project-75 by Mazagon Dock Shipbuilders Limited (MDL) in collaboration with France’s Naval Group. Though scheduled for mid-life upgrades, the critical AIP plug will not be installed during its upcoming refit at Mumbai’s Naval Dockyard, defense sources have confirmed.

AIP System Still in Trials

The fuel-cell-based AIP system, developed by DRDO’s Naval Materials Research Laboratory (NMRL) with Larsen & Toubro (L&T) as the industrial partner, is still undergoing trials and not yet deemed operational.

“We now expect the AIP to be ready by mid-2026, aligning with the scheduled maintenance of the second Scorpene-class submarine, INS Khanderi,” a senior defense official said.

Scorpene-Class Submarine Program

India currently operates six French-designed Scorpene submarines, built under Project-75 at a cumulative cost of over ₹23,000 crore. The sixth and final boat in the class, INS Vagsheer, was commissioned in January 2025.

Delays Spark Strategic Concerns

Initiated in 2014 with a projected completion in 2017, DRDO’s AIP program has overshot its deadline by nearly a decade. Originally budgeted at ₹270 crore, the delay has left all six Scorpene submarines without AIP capabilities—limiting their endurance and stealth underwater.

In response, MDL and the French Naval Group signed a new agreement on July 23, allowing for ‘jumboisation’—a complex procedure involving slicing the submarine’s hull to fit the AIP module, followed by precise reassembly to maintain structural and operational integrity.

Why AIP Matters

Diesel-electric submarines must surface every 2–3 days to recharge their batteries using atmospheric oxygen—compromising their stealth. In contrast, submarines equipped with AIP systems can remain submerged for up to two weeks, significantly enhancing survivability, surveillance evasion, and attack capability.

Rising Regional Threats

India’s maritime neighbors are modernizing rapidly. Pakistan is acquiring eight AIP-equipped Yuan-class (Hangor-class) submarines from China, while Beijing already commands the world’s largest navy with 50+ diesel-electric and 10 nuclear submarines.

India must bridge this capability gap swiftly to maintain strategic parity in the Indian Ocean Region.

Current Indian Submarine Fleet:

• 6 Scorpene-class (France)
• Old Kilo-class (Russia)
• 4 HDW-209 class (Germany)
• 2 SSBNs—INS Arihant & INS Arighat (nuclear-powered ballistic missile submarines)

INS Aridhaman, third SSBN, expected to be commissioned this year

Future Projects Still Pending:

• ₹38,000 crore proposal for three more Scorpene-class submarines
• ₹70,000 crore Project-75I for six next-generation diesel-electric submarines with AIP and land-attack cruise missile capabilities

India’s underwater warfare preparedness hinges on the successful integration of AIP technology. While DRDO’s work on indigenous systems is commendable, further delays could impact the Navy’s operational readiness. Timely execution and strategic prioritization are now critical to safeguard national maritime interests in an increasingly contested Indo-Pacific region.