DRDO’s Indigenous AIP System: India’s Defence Research and Development Organisation (DRDO) has been developing a fuel-cell-based Air-Independent Propulsion (AIP) system for several years. Recent reporting and official programme activity indicate the AIP has progressed from a land-based prototype to plans for integration into operational platforms and DRDO’s modular/scalable design is being presented as suitable not only for Kalvari-class upgrades but also for larger, next-generation conventional submarines envisaged under Project-76. This could significantly boost submerged endurance, stealth and indigenous content in India’s submarine fleet.
What is AIP, and why is it important for submarines?
Air-Independent Propulsion (AIP) is a means for a diesel-electric submarine to produce electrical power underwater without the need to surface or snorkel to run its diesel engines; therefore, its submerged endurance is extended to a great extent. A fuel-cell AIP (the method DRDO is advocating) combines hydrogen and oxygen to generate electricity in a very quiet way and with a low thermal signature, thus submarines become less detectable and more indomitable during the patrol.
AIP is a step that narrows the difference in capabilities between nuclear and conventional submarines for certain missions (patrol, surveillance, blockade) to navies that are heavily dependent on traditionally powered boats.
DRDO’s Indigenous AIP System
DRDO’s Naval Materials Research Laboratory (NMRL) proved a land-based prototype of a fuel-cell AIP system back in 2021, conducting endurance and maximum-power runs as per user requirements, an important R&D milestone in maturing fuel-cell AIP technology for Indian submarines.
Since then, the programme has moved toward integration planning and production-level activity in partnership with shipyards and industry. Separately, the MoD signed contracts in late 2024 for the construction of AIP plugs and their integration aboard Kalvari-class boats, a clear sign India is transitioning from lab prototypes to ship-level integration.
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“Scalable” AIP
When engineers call a system “scalable” they mean the module can be adapted in size/power to suit different hulls and mission needs. For submarines that could translate to stacking more fuel-cell modules or larger hydrogen/oxygen stores to serve:
- Small coastal SSKs for littoral missions
- Medium-displacement boats like modern Scorpène derivatives
- Larger hulls planned under Project-76 that demand higher continuous electrical output.
A modular fuel-cell architecture reduces re-engineering effort, shortens integration cycles and enables a single core technology to fit multiple classes, which helps cut lifecycle cost and increases the chance of higher indigenous content across the fleet. (This is the modular argument reported in recent coverage of DRDO’s work.)
Project-76
Project-76 is the aspirational Indian programme to move toward larger, more capable indigenous conventional submarines (estimates in reporting range ~3,000–4,000 tonnes submerged). These boats will demand more power for sensors, propulsion (potentially pump-jets), hotel loads and longer stealthy patrols.
A scalable AIP that can be sized-up to match the power profile of a P-76 hull removes a major barrier to fully indigenous large conventional submarine designs and helps justify the industrial and fiscal investment in an all-India design-build path. Analysts and defence writers have pointed to DRDO’s modular fuel-cell approach as directly relevant to Project-76 ambitions.
Where “90%” comes from?
Multiple official initiatives from the Indian Navy’s indigenisation plans to DRDO’s industry outreach, stress increasing local content in weapons, sensors and platform systems. Recent contracts for AIP plugs, and DRDO-industry partnerships (L&T, Thermax and others reported in the media) show a strong push toward domestic production and systems integration.
Some defence reports and opinion pieces characterise the DRDO AIP effort as capable of enabling very high levels of indigenisation (figures like “~90%” appear in commentary and industry marketing) but that number is best read as an aspirational or programme-level estimate rather than a single, independently-audited fact.
In practice, final indigenisation percentages depend on: which subsystems are counted, supply-chain maturity (cells, catalysts, power electronics, cryogenics or reformers), and whether certain niche components remain imported. Official sources emphasise the Atmanirbhar (self-reliant) goal, while media coverage highlights optimistic indigenisation projections.
Operational benefits for India’s submarine force
If successfully integrated into Kalvari-class upgrades and scaled for Project-76, DRDO’s fuel-cell AIP could deliver:
- Weeks-long submerged endurance increases (mission-dependent).
- Lower acoustic and thermal signatures compared with diesel-run charging cycles.
- Greater operational persistence in choke points and littoral waters where India needs sustained, quiet patrols.
Reduced reliance on foreign AIP suppliers and fewer platform-level integration headaches when building different boat classes domestically. Those are the tangible advantages militaries seek when investing in fuel-cell AIP.
How is the Atmanirbhar plan being implemented?
DRDO’s strategy has combined in-house design (NMRL) with industry partners and shipyards for manufacture, integration and testing. Contracts with Mazagon Dock and other Indian firms for AIP plug construction and integration (announced end-2024) signal the practical move toward production. This industrial coupling of DRDO as system developer, DPSUs/shipyards as integrators and private industry supplying subsystems is meant to scale capability while growing domestic supply chains and jobs. Expect more industry outreach, supplier qualification drives and phased serial integration as the programme matures.
What does this mean for strategic posture and exports?
A fully scaled, reliable indigenous AIP and a domestic large conventional submarine design would strengthen India’s undersea deterrence and area denial posture in the Indian Ocean. Over time, an Indian AIP stack that proves itself in trials could become an exportable module for friendly navies or for indigenous submarine programmes in partner countries, but international sales would require extended operational records and export-clearance regimes. Analysts view the move as both a sovereignty and potential economic opportunity, albeit one that will take years to materialise.
