Eight Years On, AIP System Still Not Ready

Delays in a crucial technology have caused a major setback in India’s attempts to bolster its underwater naval force. Eight years after its expected completion, India’s top defense research organization, along with a leading private industry partner, has still not made the Air Independent Propulsion / AIP system operational for use in the Scorpene-class submarines.

They began developing the AIP system in 2014 with a sanctioned budget of ₹270 crore and aimed to complete it by 2017. However, as of mid-2025, they are still testing the system, and it remains unfit for operational deployment.

Due to this delay, the Indian Navy’s first Scorpene-class submarine, INS Kalvari, which is currently undergoing scheduled maintenance at Mumbai’s naval dockyard, will not receive the much-needed AIP upgrade. This technology is crucial for extending underwater endurance and enhancing stealth capabilities—key elements in modern submarine warfare.

Without the AIP module, INS Kalvari and its sister submarines must surface or snorkel every few days to recharge their batteries, making them more visible to enemy surveillance systems. They could have stayed underwater for up to two weeks with the new fuel cell-based AIP module.

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A deal to include AIP technology into upcoming Scorpene submarines was recently signed. During this procedure, known as “jumboisation,” the submarine’s hull is cut open, the AIP plug is inserted, and the submarine is sealed back up. The process is extremely precise and scientific. However, India’s active submarines would have to do without this vital equipment for the time being.

Planned AIP System Upgrades Remain on Hold

India had earlier planned to build three more Scorpene submarines at an estimated cost of ₹8,000 crore. The government proposed six advanced submarines with next-generation diesel-electric propulsion under Project-751 at a cost of ₹70,000 crore. Officials anticipated including both land-attack cruise missiles and AIP systems in both initiatives; however, they have not yet approved either proposal in its entirety.

The next generation of Scorpene submarines, if cleared, will feature major design improvements. These include increased mission duration, improved living conditions for crew members, more storage for essentials, and enhanced sanitary systems. The weapons-carrying capacity will also be more than double that of the current fleet, allowing for a broader range of operations.

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Engineers will equip the new submarines with upgraded electric motors that they can maintain more easily and that will consume less energy. A new vendor will supply the diesel generators to improve fuel efficiency and enhance after-sales support. This change should reduce fuel usage by around 20% and lower vacuum buildup when the submarine operates near the surface.

To enhance stealth, the new design also includes features to reduce infrared heat signatures, gas emissions, and visible outlines. These upgrades aim to make the vessels harder to detect and more capable during long missions. However, until the AIP system is operational and integrated, these improvements will only go so far in closing the growing capability gap.

Pakistan Gains Edge With Fully AIP-Equipped Fleet

Pakistan is making rapid progress while India’s submarine modifications are taking longer than expected. In line with this advancement, the country is currently purchasing eight Yuan-class submarines from China. The shipyard is delivering these submarines—also known as Hangor-class—already equipped with AIP systems.

The inclusion of AIP in all new Pakistani submarines gives them a significant tactical edge. These submarines will be able to remain underwater for longer periods, making detection harder and improving their effectiveness in naval operations.

China and Pakistan are working together to help Pakistan develop a more sophisticated and powerful underwater fleet. With ten nuclear-powered and more than fifty diesel-electric submarines, China already boasts the biggest fleet in the world. India’s failure to update its underwater fleet in a timely manner puts it at a disadvantage in terms of regional maritime security as Pakistan’s fleet grows in size and capacity.

India currently owns six Scorpene-class submarines that were constructed with French assistance as part of Project-75. INS Kalvari, INS Khanderi, and the most recent, INS Vagsheer, are among them. Despite being modern, these vessels are nonetheless incapable of performing AIP.

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The rest of India’s conventional submarine fleet consists of older models—seven Russian Kilo-class and four German HDW submarines. Most of these are more than 30 years old and require regular maintenance, making them less reliable in prolonged missions.

India does have two nuclear-powered submarines with ballistic missile capabilities and a third one expected to join the fleet. In contrast to traditional submarines, these are scarce and have distinct strategic functions.

The delay in the AIP system, combined with aging conventional submarines and stalled procurement decisions, has led to an operational gap. With neighbouring countries rapidly enhancing their submarine fleets, India’s ability to maintain a strong underwater presence is under pressure.