India is set to achieve a significant milestone in its naval indigenisation program with the integration of its first indigenous air-independent propulsion (AIP) system into the Indian Navy’s fleet of submarines.

According to sources in the defence establishment, the process is scheduled to commence in mid-2026, with the system being fitted on INS Khanderi, the second submarine of the Kalvari-class (Scorpene-class), during its scheduled refit in July 2026.

This development marks a major technological leap in submarine warfare capability for India, as it will allow the Navy’s diesel-electric submarines to achieve extended underwater endurance while maintaining stealth.

The Defence Research and Development Organisation (DRDO) has been working on this niche propulsion technology, with significant contributions from industry partners Larsen & Toubro (L&T) and Thermax.

The prototype AIP is expected to be ready by December 2025, after which integration work will begin during INS Khanderi’s refit process. The integration schedule indicates that the submarine will complete its AIP refit cycle by July 2027, following sea trials expected between March and April 2027.

The trial period will be highly critical, as the new technology will be tested for reliability, endurance, and operational performance under real-world conditions.

The induction of AIP technology is fundamentally important to India’s undersea warfare capabilities. Traditional diesel-electric submarines are required to surface or use a snorkel at regular intervals to recharge their batteries, exposing them to detection by enemy surveillance assets.

In contrast, an AIP-equipped submarine can remain submerged for several weeks, ensuring far greater stealth and combat effectiveness during extended operations.

As DRDO notes, the system acts as a “force multiplier,” significantly increasing the lethality of conventional submarines without needing the complexity and cost of nuclear propulsion systems.

A particularly unique feature of the indigenous system is its hydrogen-on-demand technology. Unlike several other AIP designs worldwide that require submarines to carry stored hydrogen—a major safety hazard given the volatility of the gas—India’s design generates hydrogen inside the submarine as needed.

This innovation not only enhances safety but also greatly simplifies storage and logistics, making the solution more practical and secure for operational deployment. Moreover, the system is based on a fuel cell technology that produces water as a by-product, rendering it an environmentally friendly and sustainable propulsion solution.

The integration of AIP into INS Khanderi represents the first step in a phased process aimed at equipping the Indian Navy’s existing and future conventional submarines with this capability.

Initially, INS Khanderi will serve as the test-bed platform, and following successful trials, similar retrofits are expected to be carried out on other Kalvari-class submarines during their refit schedules.

In addition, all future indigenous submarines planned under current and upcoming naval projects are expected to be built with this AIP system by default, further boosting India’s defence indigenisation drive.

India’s entry into the elite club of nations with indigenous AIP capability—currently including countries like Germany, France, and Japan—signifies a strategic leap in self-reliance and technological sophistication.

The move strengthens India’s maritime deterrence posture, especially in the Indian Ocean Region, where stealth and sustained underwater presence are critical in countering regional rival activities.

The project also underscores the growing synergy between DRDO, domestic industry partners like L&T and Thermax, and the Indian Navy in developing and operationalising advanced defence technologies.

With the Transfer of Technology (ToT) documents for the AIP system formally handed over to L&T during Aero India 2021, the industrial ecosystem is prepared to support scaled-up production and integration.

Thus, the upcoming retrofit of INS Khanderi and subsequent projects stand as symbols of India’s steady progress towards greater self-reliance in defence under the "Make in India" framework.

In conclusion, the planned integration of India’s indigenous AIP system into INS Khanderi in July 2026 will mark a watershed moment in the evolution of the Indian Navy’s submarine force.

By enhancing endurance, stealth, safety, and sustainability, this indigenous solution will not only elevate India’s undersea warfare capabilities but also consolidate its standing as a nation capable of developing and deploying advanced, indigenous defence technologies with global relevance.

Agencies