
India has achieved a major milestone in its efforts to strengthen the Indian Navy's underwater warfare capabilities, with the inauguration of the Setting to Work Phase-2 (STW-2) activity of the indigenous Air Independent Propulsion (AIP) system.
The development marks an important step towards equipping the Navy's conventional submarine fleet with technology that will significantly enhance its underwater endurance and operational effectiveness.
The AIP Energy Module has been developed indigenously by the Naval Materials Research Laboratory (NMRL) under the Defence Research and Development Organisation (DRDO). The technology is designed to reduce the dependence of diesel-electric submarines on atmospheric oxygen, allowing them to remain submerged for much longer periods without needing to surface or snorkel for battery charging.
The inauguration ceremony was held at Larsen and Toubro's AM Naik Heavy Engineering Complex in Hazira, Gujarat. Defence Secretary Rajesh Kumar Singh, who also serves as Chairman of DRDO and Secretary of the Department of Defence Research and Development, attended the event virtually as the chief guest.
Senior officials present at the facility included Vice Admiral B. Sivakumar, Chief of Materiel of the Indian Navy, and DRDO Director General (Naval Systems and Materials) R. Balamuralikrishnan.
The commencement of STW-2 represents a critical stage in the program's progression. During the next phase, the AIP Energy Module will be energised for power production and subjected to rigorous testing in accordance with Indian Navy protocols.
Upon successful completion of these trials, the system will be handed over to Mazagon Dock Shipbuilders Limited for integration into a Kalvari-class submarine in early 2027. The retrofit is expected to provide a substantial enhancement to the Navy's existing fleet of Scorpene-class submarines.
According to the Defence Ministry, the indigenous AIP system will significantly improve the underwater endurance of conventional submarines by enabling them to operate for extended periods without relying on atmospheric oxygen. This capability reduces the frequency with which submarines need to surface, thereby lowering the risk of detection during operations.
The technology is regarded as a major force multiplier for diesel-electric submarines. Conventional submarines typically rely on batteries while submerged and must periodically approach the surface to recharge them using diesel generators. Air Independent Propulsion technology addresses this limitation by generating power underwater, enabling longer and stealthier deployments.
Speaking at the event, Rajesh Kumar Singh congratulated DRDO and its industry partners for achieving the milestone. He praised the scientific dedication and industrial cooperation behind the indigenous AIP effort, noting that the program had now translated into "productive reality on the shop floor".
He also acknowledged the consistent support provided by the Indian Navy throughout the development process, including its role in testing and validating the system at every stage of the trials.
Singh stressed the importance of maintaining momentum in subsequent phases of the project so that the Navy's planned induction schedule can be achieved. At the same time, he underscored the need to preserve "the exacting safety culture that hydrogen and fuel cell systems require without compromise".
The indigenous AIP initiative is considered a key component of India's broader drive for self-reliance in critical naval technologies. The system is based on advanced hydrogen fuel-cell technology, an area that demands stringent safety standards as well as sophisticated engineering expertise.
The program has been the result of years of collaboration between DRDO, the Indian Navy and industry partners. Earlier development phases validated the technology's performance, paving the way for the current power-generation and operational testing stage.
Once inducted, the AIP-equipped Kalvari-class submarines are expected to gain a significant stealth advantage by remaining underwater for substantially longer durations. This improvement will enhance the Navy's ability to conduct surveillance, deterrence and combat missions across the Indian Ocean Region while reducing exposure to hostile detection systems.
The latest achievement therefore represents not only a technological milestone for India's indigenous defence ecosystem but also a notable step forward in strengthening the Indian Navy's future underwater combat capabilities.
Agencies













