Air Independent Propulsion (AIP) is a technology that enables conventional non-nuclear submarines, such as India's Kalvari-class, to operate underwater for extended periods without needing to surface or use a snorkel to access atmospheric oxygen.

This capability significantly enhances their stealth and operational endurance, allowing them to stay submerged for up to 8-10 days or even nearly two weeks, compared to the few days typical diesel-electric submarines can manage without AIP.

Conventional diesel-electric submarines rely on atmospheric oxygen to run their diesel engines which charge onboard batteries. When submerged, they depend on these batteries and must surface or snorkel frequently to replenish oxygen and recharge.

Surfacing exposes the submarines to detection through engine noise and heat exhaust, compromising stealth. AIP technology drastically reduces this vulnerability by enabling the submarine to generate electricity underwater without atmospheric oxygen.

The AIP system typically generates electricity via chemical or thermal processes—commonly through fuel cells—using stored substances like hydrogen and oxygen, producing silent power that drives the electric propulsion motor directly or supplements battery charge.

This method is more efficient and quieter than running diesel engines and results in minimal exhaust emissions, which reduces the risk of detection.

In the case of India's Kalvari-class submarines:

The Defence Research and Development Organisation (DRDO) has developed an indigenous fuel cell-based AIP system renowned for high safety and performance.

Mazagon Dock Shipbuilders Ltd (MDL), the original builder of Kalvari-class subs under technology from France's Naval Group, is collaborating to integrate the AIP system.

The integration process, called "Jumboisation," involves precision cutting of the existing submarine hull, inserting the new AIP section (plug), and rejoining the structure. This increases the submarine's length and weight and requires technical oversight and training from Naval Group engineers to ensure safety and operational integrity.

The first retrofit with the AIP system is planned for INS Kalvari during its major refit, with further installations scheduled across the fleet.

The impact of AIP integration is substantial—it boosts submerged endurance from days to potentially a fortnight, greatly enhancing stealth and reducing the frequency of surfacing. This extension translates into a tactical advantage, enabling sustained underwater operations, reduced detection risks, increased stealth, and operational flexibility in complex maritime theaters.

This advancement effectively bridges the gap between traditional diesel-electric submarines and nuclear-powered ones in terms of underwater endurance and stealth, albeit without matching the raw power of nuclear propulsion.

AIP systems enable non-nuclear submarines like the Kalvari-class to produce their own oxygen-independent power underwater through fuel cells, extending their submerged endurance and stealth capabilities by minimising the need to surface for air, thereby significantly improving their operational effectiveness and survivability in hostile environments.

The ongoing retrofit program in India involving DRDO's indigenous AIP technology and MDL's shipbuilding expertise represents a major enhancement of the Indian Navy's submarine fleet.

Based On The Week's Report