🛡️ Security & DefenceMAINS · GS3.12 · GS3.20

An Indian AIP module heads for a Kalvari submarine in early 2027

DRDO's indigenous air-independent propulsion energy module entered its second setting-to-work phase at L&T Hazira, to be energised and tested before handover to Mazagon Dock for integration.

What happened

The Setting to Work Phase-2 activity of the indigenous Air Independent Propulsion (AIP) energy module, developed by DRDO's Naval Materials Research Laboratory, was inaugurated at L&T's AM Naik Heavy Engineering Complex, Hazira on 24 October 2026.
AIP boosts the underwater endurance of diesel-electric submarines by reducing dependence on atmospheric oxygen.
The Defence Secretary and Chairman DRDO attended virtually as chief guest, with the Navy's Chief of Materiel and DRDO's DG (Naval Systems and Materials) present at Hazira.
The DRDO Chairman credited scientific perseverance and industrial cooperation, acknowledged the Navy's role in testing and validating at every stage, and stressed the exacting safety culture that hydrogen and fuel cell systems require.
Next: the module will be energised for power production and tested to Indian Navy protocols before handover to Mazagon Dock Shipbuilders for integration on a Kalvari-class submarine in early 2027.

For Prelims

What AIP does: a conventional submarine must surface or snorkel to run its diesels and recharge batteries, which is when it is detectable. An air-independent source - fuel cells, Stirling engines, closed-cycle diesel or MESMA steam turbines - lets it generate power submerged, extending endurance from about a day to one to three weeks depending on design.
India's choice is a phosphoric acid fuel cell system developed by NMRL with hydrogen generated on board from a chemical reformer rather than stored - the distinguishing feature against imported designs, and the reason safety handling dominates the programme.
The Kalvari class is six Scorpene-design submarines built at Mazagon Dock under Project 75 with French transfer of technology; the AIP is to be retrofitted during a boat's refit by inserting a hull plug, which requires cutting the pressure hull.
Project 75(I) is the follow-on programme for six AIP-equipped conventional submarines under the Strategic Partnership model, distinct from the three additional Scorpenes contracted with Mazagon Dock; India's nuclear-powered boats (Arihant class) do not need AIP.
Setting to Work is the commissioning sequence for a complex system - mechanical completion, then controlled energisation and functional testing - before it is certified for integration; doing it ashore at a yard de-risks the submarine refit.
NMRL, at Ambernath, is DRDO's naval materials laboratory, responsible for AIP, fuel cells, hull and signature-reduction materials; L&T Hazira and Mazagon Dock are the private and public yards in the chain.
Why submarine endurance is operationally central for India: the Navy's conventional fleet patrols chokepoints in the Indian Ocean where an adversary's boats transit, and detectability while snorkelling is the main vulnerability of a diesel-electric boat on station.
Comparable systems: Germany's Type 212/214 use PEM fuel cells, Sweden uses Stirling engines (as in Japan's Soryu class), and France's MESMA is a closed-cycle steam system - India joining this set makes it one of a handful of countries with an indigenous AIP design.

For UPSC: A concrete indigenisation milestone with a named induction route and date, in a capability only a few countries hold. Deploy it on defence indigenisation, on naval capability and the submarine arm, and on DRDO-industry-shipyard collaboration.

What it is NOT: No power output, no endurance gain, no cost and no identification of which Kalvari-class boat will receive the module first - so "early 2027" cannot be tied to a refit schedule. Nothing on how many boats are planned for retrofit or over what period, nothing on Project 75(I) where an AIP-equipped design is the requirement, and no statement of indigenous content. The release also does not say when sea trials would follow integration, which is the milestone that would actually establish the system works.

For Mains

Syllabus: GS3.12 · GS3.20 · Linkage L2

Anchor

DRDO's indigenous AIP energy module, developed by the Naval Materials Research Laboratory, has entered its Setting to Work Phase-2 at L&T Hazira, and will be energised and tested to Navy protocols before handover to Mazagon Dock for integration on a Kalvari-class submarine in early 2027.

Substantiation (data)

AIP extends the underwater endurance of diesel-electric submarines by reducing dependence on atmospheric oxygen. The Defence Secretary and DRDO Chairman attended virtually, with the Navy's Chief of Materiel and DRDO's DG (Naval Systems and Materials) at Hazira. The DRDO Chairman credited industry cooperation and the Navy's testing and validation at every stage of trials, and stressed the safety culture that hydrogen and fuel cell systems demand.

Position

This is indigenisation in its most demanding form. AIP is a capability only a handful of countries design, India's version generates hydrogen on board rather than storing it, and the programme has run a DRDO laboratory, a private heavy-engineering yard and a public shipyard in sequence to get a module to the shop floor. Proving it ashore before a hull is cut open is exactly the right order of operations.

Counterpoint

Nothing here can be measured. No power rating, no endurance gain, no cost, no boat named and no sea-trial date - and for a submarine programme, integration is the beginning of the test rather than its end, because the module must work in a pressure hull under operational conditions. Retrofit by hull plug also takes a boat out of an already thin conventional fleet for an extended refit, and the release says nothing about how many boats or over what period.

Way forward

State the power output and expected endurance gain, the retrofit sequence across the class, and the sea-trial timeline after integration. Settle how the indigenous AIP relates to Project 75(I), where an AIP-equipped design is a requirement - buying one abroad while proving one at home needs an explicit answer.

Conclusion

A genuine milestone in a capability few countries hold, moving from laboratory to shipyard on schedule. The numbers that would prove it works are still to come.

Deploys into: Defence indigenisation and DRDO · Naval capability and the submarine arm · Public-private defence manufacturing · Fuel cell technology

Ministry of Defence · 2026-10-24 · PRID 2328040 · PIB source ↗