India is getting ready to add its first indigenous air-independent propulsion (AIP) system to a submarine, starting in mid-2026.
The upgrade will begin with INS Khanderi, a Kalvari-class submarine, during its scheduled refit. This new system will allow the submarine to stay underwater for longer periods without surfacing, giving the Navy stronger stealth and combat power.
INS Khanderi to Get DRDO’s AIP Upgrade in 2026
India is preparing for a big step forward in its naval indigenisation program by fitting its first indigenous air-independent propulsion (AIP) system into a submarine.
The work is set to begin in mid-2026, starting with INS Khanderi, the second boat of the Kalvari-class (Scorpene-class). The submarine will undergo its scheduled refit in July 2026, and that’s when the system will be integrated.
Why This Matters
This is a major technological upgrade for the Indian Navy. AIP will allow its diesel-electric submarines to stay underwater for much longer without needing to surface, while also maintaining stealth.
Currently, conventional submarines must come up to the surface or use a snorkel frequently to recharge their batteries, which increases the risk of being spotted. With AIP, submarines can stay submerged for weeks at a stretch, giving them far better stealth and combat power.
Development of the Indigenous System
The Defence Research and Development Organisation (DRDO) has been leading the project with strong support from Larsen & Toubro (L&T) and Thermax.
A prototype AIP system is expected to be ready by December 2025.
Integration with INS Khanderi will start during its 2026 refit
Sea trials are expected in March–April 2027.
The full refit process should be finished by July 2027.
These trials will be crucial to check how well the system performs in real-world conditions.
What Makes India’s AIP Special
A key highlight of India’s AIP is its hydrogen-on-demand technology.
Many AIP systems worldwide need submarines to carry hydrogen on board, which is risky and unsafe because hydrogen is highly flammable.
India’s design generates hydrogen inside the submarine only when needed, making it much safer and easier to handle.
The system is based on fuel-cell technology, which produces water as a by-product—making it clean, eco-friendly, and sustainable.
This innovation not only improves safety but also simplifies logistics for long naval missions.
The Bigger Plan
INS Khanderi will be the test-bed for the system.
If successful, other Kalvari-class submarines will also get AIP upgrades during their refits.
Future Indian submarines under development will come pre-equipped with AIP by default.
This phased plan ensures that both current and future fleets benefit from the new technology.
Strategic Importance
With this step, India joins an elite group of nations—including Germany, France, and Japan—that have developed their own AIP systems.
The upgrade will strengthen India’s ability to maintain a stealthy underwater presence in the Indian Ocean Region, a critical area where rival navies are becoming more active.
It acts as a “force multiplier”, improving combat power without the cost and complexity of nuclear submarines.
It also highlights the growing partnership between DRDO, Indian industry (like L&T and Thermax), and the Navy in developing advanced defence technology.
Industry Readiness
India has already taken steps to scale up production. During Aero India 2021, DRDO formally handed over the Transfer of Technology (ToT) documents for the AIP system to L&T, preparing the industry for large-scale integration.
The integration of the indigenous AIP system on INS Khanderi in July 2026 will be a milestone moment for the Indian Navy.
By improving endurance, stealth, safety, and sustainability, this technology will:
Boost India’s undersea warfare capability,
Strengthen its defence indigenisation drive under Make in India, and
Prove that India can design and deploy advanced defence systems with global relevance.
